In this study, the actions of Pseudomonas phospholipase C (EC 3.1.4.3) were investigated with respect to their toxicity and effect on blood coagulation. Phospholipase C (P. fluoresces) is an effective inhibiter of thromboplastin and probably uses this enzyme as a therapeutic or prophylactic agent in thrombosis and other forms of intravascular coagulation. Phospholipase C (P. fluorescens) purified by us caused significant loss in the procoagulant activity of thromboplastin. Gram-negative phospholipase C with subtoxic or weakly toxic doses inhibited blood coagulation in rabbits for up to 60–180 min after i.v. infusion of the enzyme.