Three anticoagulant proteins were isolated from the venom of Naja nigricollis (spitting cobra). The peaks of anticoagulant activity co-chromatographed with phospholipase A2 activities. The three proteins were homogeneous by the criteria of electrophoresis in two acidic polyacrylamide gel systems. Electrophoresis in sodium dodecyl sulfate also yielded single protein bands with molecular weights of about 15,000. The amino acid compositions of the three anticoagulant proteins are reported. All three proteins have only one amino acid replacement in the first 25 to 30 amino acids of their NH2-terminal sequences, compared to the sequence of the basic phospholipase from N. nigricollis venom. Removal of Ca2+ from the crude venom caused loss of both anticoagulant and phospholipase activities, and restoration of Ca2+ caused partial recovery of both activities. Both activities were lost in parallel when the venom was heated between pH 6.0 and 8.5. The association of the anticoagulant effect with phospholipase activity contradicts the previous conclusion that phospholipase is not responsible for the anticoagulant action of cobra venom. The previous results might be explained by independence of the anticoagulant and phospholipase effects within the same protein molecule, or by different activity levels of monomer and dimer forms of the enzyme.