The pharmacokinetics and pharmacodynamic effects of intravenously injected (0.06 U/kg) human biosynthetic insulin of recombinant DNA origin and purified porcine insulin, both regular, were compared in 10 healthy volunteers. Both had identical immunological properties. Some of their pharmacokinetic features, such as total plasma clearance and bioavailability, were similar, but they appeared to differ in biological half-life, elimination rate constant and apparent volume of distribution. No appreciable difference was found between their hypoglycaemic activity and their inhibitory effect on endogenous insulin secretion. However, hyperglucagonaemia seemed to be less pronounced after human biosynthetic insulin than after purified porcine insulin. These findings are discussed by comparison with the results of other studies on human biosynthetic insulin.