The therapeutic efficacy of human insulin (recombinant DNA) was compared with that of purified porcine insulin (PPI) in seven male subjects with previously treated insulin-dependent diabetes mellitus. In a random crossover design the patients received either PPI or human insulin during one of two consecutive 7-day periods of intensive insulin therapy. Control was evaluated on days 6 and 13. Tissue sensitivity and responsiveness to the study insulins were determined by insulin dose-response studies performed using the euglycemic glucose clamp on days 7 and 14. Insulin dose and all measures of control on days 6 and 13 were not statistically different between treatments. When the insulin dose-response studies during each treatment were compared there were no differences between them. Thus, in previously treated patients with insulin-dependent diabetes, undergoing brief but intensive insulin therapy with continuous subcutaneous insulin infusion, human insulin is as clinically efficacious as PPI. Furthermore, insulin sensitivity and responsiveness, as assessed by dose-response studies during the euglycemic glucose clamp were equivalent for both insulins.