(MONEY Magazine) – Who wouldn't want an anti-impotence drug that lasts 24 hours? Samuel Isaly, manager of Eaton Vance Worldwide Health Sciences fund, recently scooped up shares of Icos (ICOS), maker (with Eli Lilly) of Cialis, a drug for erectile dysfunction that lasts six times longer than Pfizer's blockbuster, Viagra. While the jury's still out on whether Cialis can knock Viagra from its perch, Isaly notes that Cialis has had brisk sales in Europe since its launch earlier this year, and that Cialis may have an edge with younger people. "Pfizer used Bob Dole and that gets locked in people's memory," he says.

Shares of Icos rose to $45 in June on news of Cialis' strong overseas sales and in anticipation of FDA approval by year's end. But in August, the stock price slid to $33 after the company said that higher costs to market the drug could hurt earnings in 2004.

Given the volatility of biotechs, potential Icos investors should tread cautiously. But shareholders should hold steady: Isaly is confident that this unprofitable company will be making money by 2005. --ERICA GARCIA