Chronic zinc deficiency causes a delay of reparative processes. The rate of repair is normalized by the administration of zinc. An acute lowering of the serum zinc level follows trauma. In a previous experimental study, it was demonstrated that the intramuscular administration of zinc beginning before trauma results in an increased collagen accumulation in early granulation tissue. In this study, the rate of collagen synthesis was determined to see if the higher amount of collagen found in early granulation tissue could be explained by increased collagen synthesis. The rate of collagen synthesis was studied by the determination of the incorporation of 14C-L-proline into collagen in vivo and in vitro. No difference was found regarding collagen synthesis in the granulation tissue of rats in the control and zinc treated groups. Specific activity of collagen, a measure of newly synthesized collagen in relation to the total amount of collagen, was found to increase markedly during the observation time. Further, the specific activity was found to be lower in the rats of the zinc treated groups than in the rats of the control groups on days 4 and 5, an indication that, after the administration of zinc there is more earlier synthesized, not labeled, collagen present. A possible explanation is that there is a concomitant synthesis and breakdown of collagen in granulation tissue and that the rate of breakdown is decreased by the administration of zinc.