The study was concerned with the comparison of the action profile of regular and NPH preparations of human insulin (recombinant DNA) and of PPI (pork purified insulin). In addition, the action profiles of some mixtures (10:90, 15:85, 20:80, 25:75, 30:70) of regular and NPH human insulin were evaluated. The comparisons were based on the Gerritzen test. There was no statistically significant difference in the time-course of the blood glucose levels after administration of NPH human insulin and NPH PPI. A tendency was noted, however, that NPH human insulin has a faster onset of action and that the serum glucose minimum for NPH human insulin lasts longer. The serum glucose curves after the application of regular and NPH human insulin initially lie closer together than after the respective PPI preparations. In the later phase, regular human insulin interferes less with the NPH curves. This means that combinations of regular and NPH human insulin may have a clinically useful action profile. No skin reaction or other adverse reaction was detected after application of human insulin and no antibodies against human insulin and Escherichia coli protein were found.