Doctors said the first potentially effective treatment for strokes, which could help as many as 80 percent of those suffering strokes caused by blood clots, became available Monday on an experimental basis.

Emory University Hospital, which announced availability of the treatment, said Atlanta is one of nine U.S. cities approved for participation in a study of tissue plasminogen activator or t-PA, a clot-dissolving substance that occurs naturally in the body.Carol Barch, a member of the team studying t-PA, said the experiments with the treatment were initially carried out in Cincinnati, where it was "very successful."

"This is the first time a treatment has been available for victims of stroke," she said. "Previously, doctors could only treat the symptoms."

Dr. Bruce Mackay of Grady Memorial Hospital said that if certain stroke victims receive t-PA within 90 to 180 minutes of a stroke, it can dissolve potentially lethal blood clots, save lives and minimize damage to the brain.

"No drug or doctor will ever be able to help if a person does not recognize stroke symptoms," he said. "People must learn these and get immediate medical attention so we have a chance to help."

The earlier doctors can open a blood vessel with the t-PA agent, "the more brain we are able to preserve."

Barch said stroke symptoms include severe dizziness, dimness or loss of vision in one or both eyes, severe headache, a sudden severe headache, difficulty in speaking or understanding the speech of others, and numbness or weakness on one side of the body. All of the symptoms occur suddenly.

The t-PA stroke study is sponsored by the National Institutes of Health. Emory University and other hospitals in Atlanta will participate in the investigation of the treatment on blood clot-induced stroke.

A stroke can be caused either by a clot blocking a vessel in the brain or by a blood vessel in the brain bursting. Mackay said t-PA cannot help victims of burst vessels but may help the 80 percent of victims whose strokes are caused by clots.