NEW YORK (CNN/Money) - Wave after wave of takeovers has swept through the nation's ever-consolidating drug industry, leaving many in the business to ask: Which company will be next?

The immediate answer is Pharmacia, which has agreed to be bought by Pfizer and soon may join companies including Upjohn, Warner-Lambert and SmithKline Beecham that have merged with someone else.

But drugmakers long identified as buyout targets -- Bristol-Myers Squibb, Schering-Plough and Wyeth -- have remained independent even as their stocks have fallen. And long-expected deals have been slow in coming, leading some industry experts to give up on the game of predicting when the next merger will come, or who will be involved.

"I guarantee you there will be more M&A," said David Saks, who runs the Saks Medscience Fund, a hedge fund, referring to mergers and acquisitions. "I can't tell you when."

Bigger drug companies, it's argued, have power of scale. They can spend more on research to find new drugs that then are easier to sell with their hefty marketing muscle. That's the unofficial mantra at Pfizer, which became the world's No. 1 drugmaker through acquisitions.

The relatively modest market values of Bristol, Schering and Wyeth make them all takeover targets in a fragmented industry where the combined Pfizer and Pharmacia will have just 11 percent of worldwide sales, industry analysts say. Pharmacia agreed last summer to be bought by Pfizer for $60 billion in a deal expected to close this month.

Wyeth (WYE: Research, Estimates) has a $45 billion market value and Bristol-Myers' (BMY: Research, Estimates) value is $43 billion. That's nearly twice the size of Schering-Plough, whose market cap got whittled to $23 billion by a profit warning last week.

But none of the companies is trading as if it's a target. Bristol-Myers shares are off 7 percent this year after tumbling 55 percent in 2002. Down 39 percent last year, Wyeth stock has fallen another 10 percent in 2003, and Schering-Plough is off 28 percent this year after a 37 percent drop in 2002.

To be sure, drug mergers aren't the only deals suffering. The entire market for mergers and acquisitions has slumped since 2000, when a record $1.7 trillion in deals were announced in the United States, according to Thomson Financial. Announced deal values fell to $433 billion last year, off 75 percent from the peak.

"The question you have to ask is: Who will buy them?" said Mara Goldstein, who covers the drug industry for CIBC World Markets.

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A third big acquisition is unlikely for Pfizer (PFE: Research, Estimates), which is set to digest Pharmacia and swallowed Warner-Lambert in 2000.

Johnson & Johnson (JNJ: Research, Estimates), the No. 2 drugmaker by market value, is acquisitive but prefers smaller deals. For example, it agreed to buy Scios Inc., a California-based biotechnology company, for about $2.4 billion last month. Merck (MRK: Research, Estimates), the No. 3 drugmaker by market value, favors licensing deals to takeovers.

Not all is dormant. Switzerland's Novartis AG (NVS: Research, Estimates) has spent $2.1 billion to raise its voting stake in Roche to 32.7 percent, signaling it may want to swallow its rival.

The most recent large deal came when Amgen (AMGN: Research, Estimates), the No. 1 biotechnology company, bought Immunex last year for $16 billion to get the company's rheumatoid arthritis drug, Enbrel.

Expect more small biotechnology companies to be bought, said Tom Burnett, president of Merger Insight, as big drugmakers seek access to treatments that smaller biotechs would have difficulty marketing on their own.

One such name mentioned by industry experts: QLT Inc. (QLTI: Research, Estimates), which makes Visudyne, a treatment for blindness. Analysts also call Tanox Inc. (TNOX: Research, Estimates), a company that makes the asthma treatment Xolair, a potentially attractive target.

Ribapharm Inc (RNA: Research, Estimates), which developed Ribavirin, an antiviral drug that Schering-Plough markets, also has been named as a buyout candidate. BusinessWeek last month reported that ICN Pharmaceuticals (ICN: Research, Estimates) may buy back the piece of Ribapharm it spun off last year. ICN could not immediately be reached for comment.

Three years of sinking stock prices may be slowing deals. But the takeover business also suffers a perception problem. The acquisitive strategy that built companies like Tyco International (TYC: Research, Estimates), General Electric (GE: Research, Estimates) and AOL Time Warner (AOL: Research, Estimates), which owns CNN/Money, has lost favor as investors question the wisdom of growth by acquisition.

David Saks, of the Saks Medscience Fund, uses the analogy of the New York Yankees, who have the highest payroll in Major League Baseball but last won a championship in 2000. "That doesn't guarantee them a World Series," he said of spending big money.

As for Schering-Plough, Bristol-Myers and Wyeth, each company has problems that may deter buyers.

Schering's loss of patent protection for its allergy drug Claritin, with annual sales that once reached $3 billion, has cut revenue and forced the company to warn twice about profits. Investigators also are looking into a mysterious October tumble in Schering-Plough stock that came when the company met privately with an institutional investor. Days later, the company cut profit guidance.

Schering-Plough Wednesday said federal regulators may sue the company and its CEO over allegations the company revealed information to institutional investors ahead of the general public.

As for Wyeth, the drugmaker last month said data from an initial study showed that its hormone replacement therapy Prempro suffered another setback. Wyeth also faces litigation costs over its diet drug fen-phen, which federal regulators pulled from the market in 1997 amid concerns over the drug's safety.

Bristol-Myers, meanwhile, invested nearly $2 billion in ImClone Systems (IMCL: Research, Estimates), whose unsuccessful application for a new cancer drug ignited a scandal that enveloped former ImClone CEO Sam Waksal and Martha Stewart. Federal regulators also are investigating whether Bristol inflated profits by coaxing wholesalers to buy surpluses of its drugs.

"Nobody wants to buy into a government probe," said Morton Pierce, head of mergers and acquisitions at law firm Dewey Ballentine.

Year-to date dollar values of announced deals in the drug industry have fallen every year since 2000, data from Dealogic show.

But that hasn't kept an industry group from forecasting change. A survey of the Philadelphia Chapter of the Association for Corporate Growth released earlier this year found 97 percent of its members believe that overall merger and acquisition activity will increase in 2003.

Those forecasts eventually may prove right. Until then, a drug industry known for getting together may be going it alone.