Odd as it seems, those buy recommendations issued by professional stock analysts aren t generally worth heeding. Sell recommendations, however, should be taken seriously.

Scores of long-term studies performed over the past two decades have produced conflicting findings on analyst recommendations. Bundle the evidence together, though, and three themes emerge. First, analysts, like most investors, tend to favor glamour stocks, or ones with fast growth in sales and profits and plenty of share price momentum, but often with lofty valuations to match. Such stocks do best in rising markets, so whether a particular study says flattering things about analysts abilities depends heavily on the time period it considers. Second, changes in recommendations are far more telling than the consensus level of recommendations, most likely because the former reflect fresher information. Third, sell recommendations are far more accurate than buys.

Why might analysts give better advice when they go negative? Most likely, it s because sell recommendations are so rare that analysts who use them tend to have good reason. SmartMoney.com s database ranks stocks by their consensus recommendations with a score of 1 ( strong buy ) to 5 ( sell ). Barely 300 companies have scores between 3 and 5, versus more than 4,100 with scores between 1 and 3.

Below are three companies analysts overwhelmingly frown on. Each is covered by at least five analysts and has an average recommendation score of between 3.5 and 5.

Eastman Kodak

Once a dominant supplier of photographic equipment, Eastman Kodak has spent the digital age bleeding cash. Analysts say it likely tore through more than $600 million last year, and that although a giant pension liability makes the company difficult to assess, the liquidation value of its tangible assets is probably negative. In September, Kodak received funding from KKR, a private-equity fund best known for pioneering high-leverage buyouts like that of RJR Nabisco in 1989. Kodak is paying dearly for the funds and is likely to dilute the value of its shares, reckons Deutsche Bank. Financial forecasts for Kodak are modest, but perhaps not modest enough. The company has fallen short of Wall Street s sales and earnings estimates in each of the past four quarters.

Beazer Homes

On Jan. 5, builder Beazer Homes reported a pick-up in new-home orders during the fourth quarter of 2008, but the firm also said it would issue a massive amount of stock and convertible bonds to cover debt it must repay next year. The transaction represents a 45% increase in outstanding shares, which of course dilutes the value of existing shares. Remarkably, shares have fallen only 7% or so in value since the announcement. Perhaps investors view the company s stock market value of less than $200 million as tiny enough when viewed against signs the housing market is recovering, but fourth-quarter house orders were supported by massive government perks. Sales during the second half of this year, after many of the perks have expired, will be more telling.

Sears Holdings

On one hand, Sears Holdings, parent of Sears and Kmart, trades at a worrisome 42 times this year s earnings forecast. On the other hand, the company s stock market value is barely one-quarter of its sales. As the disparity in those figures suggests, profit margins for the nation s fourth-largest mass merchant are pitiful. It turns little more than a penny of each sales dollar into operating profit, versus close to six cents for Wal-Mart. The outlook for Sears Holdings brightened a bit on Jan. 7, when management announced that sales at longstanding stores rose a fraction of a percent during the holiday season, on a 5.3% improvement at Kmart. One analyst issued a research report that day saying he was throwing in the towel on the stock, changing his recommendation to hold from sell.

A previously published version of this article misstated an estimate of Eastman Kodak's 2009 cash consumption. Analysts say the company likely went through $600 million, not $600 billion.