Gene therapy holds promise for treating diseases from cystic fibrosis to diabetes. But safely and effectively delivering genes to the cells that need them has been the field's biggest obstacle. Luyi Sen, a cardiologist at the University of California, Los Angeles's David Geffen Medical School, has a technique that could help: she uses small electric shocks to "push" the genes into cells. Scientists have long employed electric shocks to transfer genes into cells in research labs, but the voltages used would damage whole organs. Sen has lowered those voltages by placing electrodes in contact with a patient's tissues. She arranges 32 to 128 electrodes in a "basket" on a catheter or endoscope and threads the tube through blood vessels into the interior of an organ, where the basket is expanded. Therapeutic genes in solution are fed through another vessel, and tiny electric jolts induce cells to take up the genes. In tests on rabbit hearts, genes have been transferred at up to 75 percent efficiency. Today's most popular gene delivery method, viruses made noninfectious, has top rates of only 70 percent and can cause dangerous immune reactions. Several firms have expressed interest in manufacturing Sen's devices.