research holds extraordi-nary therapeutic promise. But because of the prominence of the genetic revolution and the rapid discovery of new genes, much of the public believes that gene therapy is already a viable therapeutic option for treating many serious and lifethreatening diseases. Yet in fact, while hundreds of clinical investigations involving gene transfer have been proposed in the United States, there is still no statistically significant data demonstrating long-term therapeutic benefit. This is neither surprising nor a cause for alarm. Of the 313 clinical trials registered with NIH ORDA to date, 247 (78 per-cent) involve Phase I studies designed to assess safety and potential side effects, not therapeutic efficacy. Similarly, 28 (9 percent) are Phase Il studies that involve a large number of patients, but are designed to assess safety and relative effec-tiveness. Only 2 (1 percent) of the clinical trials proposed have progressed to Phase