PREVIOUS studies from this laboratory showed perplexing wound-tensile strengths in diabetic rats.1 Three groups of animals with alloxan-induced diabetes were studied, and the results are shown in Fig 1. No explanation for the superior healing in the well controlled diabetic animals were found. These results prompted this study of the effect of insulin on wound tensile strength in normal animals. Methods Male albino Wistar rats weighing from 200 to 300 gm were used. Preliminary insulin tolerance experiments were done. Starting at 3 units/day of protamine zinc insulin suspension, 21 animals were given progressively larger doses of insulin. They were maintained for three to four days on 5, 8, 12, and 15 units of protamine zinc insulin suspension. At 15 units of insulin per day, death occurred in approximately one third of the group. The surviving animals showed an average weight gain of 80% over their initial weight after 18