Urogastrone, a human peptide growth factor that is closely related by its amino acid sequence to mouse epidermal growth factor, has been prepared by recombinant DNA techniques. The powerful mitogenic activity of urogastrone led us to evaluate its potential as an aid to wound healing. We have used the repair reaction that follows transection of the Achilles tendon in the rat to evaluate the action of urogastrone in this model. Twice-daily injections of recombinant urogastrone (20 .mu.g/kg) close to the site of the wound led to more rapid increases in the dry weight of the repair lesion and its collagen and DNA contents compared with those in saline-injected controls (5 days). At 15 and 30 days after surgery the urogastrone-treated lesion continued to show enhanced dry weights and collagen contents, whereas the DNA content declined to that of saline-treated lesions. When urogastrone treatment was stopped after 15 days, the repair lesions examined at 30 days were little different from those in animals untreated throughout. Our results provide encouragement for an eventual clinical assessment of recombinant urgastrone in humans as an aid to wound healing provided that satisfactory answers are found to several outstanding questions.