To compare the pharmacokinetics of two different concentrations, containing either 40 or 100 IU/ml of short-acting human insulin (Velasulin HM), intermediate-acting human insulin (Insulatard HM), or an insulin mixture (25% short-acting insulin, 75% intermediate-acting insulin; Mixtard HM), three randomized, single-blind, crossover trials were performed using the euglycemic clamp technique. Eighteen healthy volunteers received insulin of either formulation subcutaneously in each of the studies (15 IU Velasulin, 20 IU Insulatard, or Mixtard). The blood glucose levels were maintained constant by glucose infusions. In the trial using Velasulin, the two different insulin concentrations were equivalent regarding the total absorption [area under the curve (AUC) of serum insulin: 126 +/- 28 and 123 +/- 35 mU/l x 12 h for U40 and U100 (mean +/- SD)], but not in regard to the rate of absorption (t max 1.3 +/- 0.4 and 2.4 +/- 1.0 h for U40 and U100). In the case of Insulatard, total absorption was not equivalent (AUC 153 +/- 35 and 128 +/- 37 ml/l x 24 h for U40 and U100), but the rate of absorption was equivalent (t max 4.8 +/- 2.9 and 5.3 +/- 4.6 h). In the Mixtard series, total absorption was equivalent (AUC 142 +/- 32 and 128 +/- 22 mU/l x 24 h), but the rate of absorption was not (t max 2.2 +/- 0.9 and 3.2 +/- 4.2 h for U40 and U100). The glucose requirement was not equivalent in each of the three series.(ABSTRACT TRUNCATED AT 250 WORDS)