Slime produced by S. epidermidis strain KH 11 was extracted with phenol-saline. The saline phase was fractionated on a DEAE-Sepharose CL-6B column. The crude slime solution and its phenol-saline fraction were found to possess anticoagulant properties. They inhibited the coagulation of human plasma by thrombin, prolonged the activated partial thromboplastin time, but did not change the rate of plasma coagulation by reptilase. The anticoagulant effect of slime could be neutralized by rather high concentrations of protamine sulphate. In the presence of plasma, the staphylococcal slime also inhibited in a concentration dependent fashion the amidolytic activity of thrombin and factor Xa against synthetic chromogenic substrates. Both antithrombin III (AT III) and other plasma component(s), presumably heparin cofactor II, were required for the full expression of the slime effect. The anticoagulant action of slime was markedly less AT III dependent than that of heparin. The activity was resistant to heating (100 degrees C, 30 min). Slime and its fractions were stronger inhibitors of thrombin than of factor Xa. Fraction IV separated by DEAE-Sepharose chromatography and particularly rich in galactose and glucuronic acid had the highest inhibitory potency. It is conceivable that slime component(s) similar to glycosaminoglycans from other sources can carry the anticoagulant activity.