24 h profiles of free insulin and glucose were determined in insulin-dependent diabetic patients on intensive insulin regimens with biosynthetic human insulin, either as continuous subcutaneous insulin infusion (CSII) with mealtime bolus doses (n = 6), or intensified conventional insulin therapy (ICIT) with preprandial injections of regular insulin and intermediate-acting insulin at bedtime (n = 6). The free insulin profiles were similar to the normal profiles but there were some important differences: CSII gave hyperinsulinaemia at daytime compared to normal people (p less than 0.05) and also to ICIT (p less than 0.005); ICIT but not CSII gave hyperinsulinaemia at midnight (p less than 0.05) whereas fasting free insulin was too-low to keep blood glucose normal; the insulin peaks after the bolus doses were retarded with a maximum after 30-90 min and a return to the basal level after 5-7 h (ICIT) or 8-9 h (CSII). The height of the insulin peaks were of similar magnitude at all meals and did not differ significantly between ICIT, CSII, and normal people. Time-to-peak was dependent on the injection level. We conclude, that intensive regimens with biosynthetic hum insulin do not give normoinsulinaemia but insulin profiles that resemble physiology. Biosynthetic human NPH insulin may be rather short-acting for overnight glucose control. The interval that should be recommended between preprandial insulin dose and meal may vary depending on the preinjection insulin level.