This paper reviews all available data on thymopentin derived from the extensive preclinical safety program; most of those studies have been concluded, only the carcinogenicity studies are nearing completion. The overview also compiles the safety parameters generated from patients treated with thymopentin for different clinical conditions; in some cases treatment lasted for 12-24 months (56 patients). Different doses and modes of administration were used. The percentage of patients with side effects was comparable to the incidences in the placebo groups. Thymopentin was also well tolerated when administered concomitantly with a long list of drugs given for other reasons. The overall conclusion in that thymopentin is a safe compound.