The plasma lipolytic and anticoagulant activities following i.v. injection of either standard heparin or low molecular weight heparin (PK 10169) were compared in a study involving 10 healthy volunteers. The total lipolytic activity (lipoprotein lipase + hepatic lipase) released by PK 10169 was similar to that released by standard heparin when low molecular weight heparin was administered in doses 3- to 5-fold higher (by weight) than standard heparin. There was a dose-response relationship between the amount of PK 10169 injected and the level of plasma lipolytic activity. With doses of PK 10169 lower than 20 mg or heparin lower than 6 mg, lipolytic but not anticoagulant activity was observed. With doses higher than 20 mg with PK 10169 and 6 mg with heparin, both lipolytic and anticoagulant activities appeared. In doses where the lipoprotein lipase activities released by the 2 heparins were similar, the hepatic lipase released with low molecular weight heparin was significantly higher than with standard heparin.