Encysive ( ENCY) fans are crossing their fingers that history won't repeat itself. For the second time this year, the Houston-based biotech has a chance to get regulatory approval of its new treatment for pulmonary arterial hypertension. The Food and Drug Administration is set to decide on Monday whether the drug, known as Thelin, should be cleared for use by patients who suffer from the disorder. The agency last spring withheld final approval of the drug, shocking many who had banked on a favorable ruling. The decision hammered Encysive shares and intensified the fierce competition between Encysive and Westminster, Colo.-based rival Myogen ( MYOG). Both companies have spent years developing new drugs to serve the small but potentially lucrative PAH market. Now, assuming the company gets good news Monday, some experts still expect Encysive to win that race -- even if Myogen follows up later by introducing a better drug of its own. "We have always been confident in Thelin's approvability based on the statistically significant benefit demonstrated by the drug in a large Phase III trial," Oppenheimer analyst Cory Kasimov wrote in a research note published earlier this week. "Moreover, our confidence is enhanced by the recent positive recommendation for approval in the European Union on June 2 and the FDA's acceptance of Encysive's response as a two-month Class 1 resubmission on June 15 -- as opposed to a six-month Class 2 or an outright non-acceptance." That said, approval of Encysive's drug is hardly a sure thing. For starters, investors don't really know why the FDA withheld full approval of Thelin in the first place. The company offered no details about the FDA's concerns, a silence that took a huge toll on its stock. The shares lost half their value in a single day and later hit a three-year low before recovering some ground on more positive regulatory developments last month. Showing that anxiety remains, the stock tumbled 4.4% Thursday, as investors grew increasingly nervous about the possibility of another setback. Kasimov acknowledges that a second "approvable" letter from the FDA -- reflecting conditional rather than outright approval -- could once again trigger a "precipitous drop" in the shares. But he expresses confidence in the company's chances this time around and recommends buying the shares. Kasimov has a $9 price target on Encysive's stock, based on what he calls "conservative assumptions" for Thelin sales. His firm makes a market in the securities of both Encysive and Myogen. Encysive rose 7 cents Friday to $6.28.