GenVec Inc., a Gaithersberg biotechnology company, said yesterday that it is likely to abandon an experimental treatment for poor blood circulation in the legs after it failed to prove effective in human tests. The move would significantly reduce the potential market for BioBypass, a gene-based product designed to trigger new blood vessel growth.

BioBypass did not benefit patients with inadequate blood flow significantly more than did a placebo, the company said. The early-stage test included 107 patients who suffered from a hardening or obstruction of the leg arteries, a painful condition that increases the risk of heart attack and stroke.

GenVec's apparent desertion of BioBypass as a treatment for leg arteries still leaves the company with a shot at commercializing it as a medication for chronic heart disease, said Alexander A. Hittle, an analyst at A.G. Edwards & Sons Inc., which has an investment banking relationship with GenVec. In November, the company said human tests showed that BioBypass was a safe and effective treatment for the heart condition.

The results were less impressive for patients given BioBypass for clogged leg arteries. Test subjects walked the same distances on a treadmill as those treated with a placebo, said Henrik S. Rasmussen, senior vice president of clinical research at GenVec. Endurance while walking on a treadmill -- which produces acute leg pain in those with poor blood flow -- is the principal measure of the treatment's success. Previous tests of BioBypass in patients with clogged leg arteries showed encouraging results but lacked a large group of patients who took placebos.

"This was a large part of the cardiovascular market," said GenVec spokeswoman Mary P. Sundeen. "Now we are left to focus on the heart."

Before GenVec can obtain Food and Drug Administration approval for BioBypass as a heart disease treatment, the drug will require extensive human testing, which could take years.

Doctors inject BioBypass directly into damaged human tissue in a process known as gene therapy. GenVec would not release precise data from the most recent tests but said doctors injected patients with BioBypass 20 times.

Without BioBypass for use in the legs, GenVec will have one less treatment to lure potential business partners. Besides BioBypass, GenVec is developing only two other products: TNFerade for cancer and PEDF for blindness.

With about $23.5 million in cash and short- and long-term investments, according to its Sept. 30, 2002, filings with the Securities and Exchange Commission, GenVec has about a year's worth of cash on hand. Shares of GenVec closed yesterday at $2.84, down 8 percent.

GenVec chief executive Paul H. Fischer has said the company plans to push forward with larger human tests of BioBypass in patients with severe coronary artery disease.

Last year, Pfizer Inc., the world's largest drugmaker, ended an agreement with GenVec to co-develop BioBypass. At the time, Pfizer said it was a business decision, not a scientific one.