Three distinct fibrinolytic enzymes have been purified from the venom of Crotalus basiliscus basiliscus (the Mexican west coast rattlesnake). The high-performance liquid chromatography-based purification comprised the following steps: (a) hydrophobic interaction chromatography; (b) hydroxylapatite chromatography; (c) anion-exchange chromatography. Following hydrophobic interaction chromatography two fibrinolytic activity peaks were detected, Cbfib1 and Cbfib2. Cbfib2 was rendered homogeneous following hydroxylapatite chromatography. Upon hydroxylapatite chromatography Cbfib1 was shown to consist of two components, Cbfib1.1 and Cbfib1.2. Both Cbfib1.1 and Cbfib1.2 were purified to homogeneity using anion-exchange chromatography. SDS-polyacrylamide gel electrophoresis revealed that Cbfib1.1 and Cbfib1.2 had similar molecular weights (approximately 23,500), whereas Cbfib2 displayed a molecular weight of approximately 22,500. The enzymes do not appear to be glycosylated. Tryptic digests of all three enzymes, analyzed by high-performance reverse-phase chromatography, suggest that Cbfib1.1 and Cbfib1.2 are closely related and different from Cbfib2. The latter displayed more similarity with Cbfib1.2 than with Cbfib1.1. Specific fibrinolytic activity for all three enzymes was very similar, but general proteolytic activity varied substantially with Cbfib2 showing a 12-fold higher specific proteolytic activity when compared to Cbfib1.1 and Cbfib1.2. None of these enzymes exhibited hemorrhagic activity when injected (up to 100 micrograms) subcutaneously into mice. Cbfib1.1 and Cbfib1.2 action against fibrinogen was directed equally against both the A alpha- and B beta-chains. Against fibrin the rate of degradation of the alpha-chain was considerably higher than that of the beta-chain. Cbfib2 showed mainly alpha-fibrin(ogen)ase activity with limited activity on the beta-chain. Several fibrinogen cleavage sites on the A alpha-chain have been identified: Cbfib1.1 and Cbfib1.2 cleave at Lys413-Leu414, Ser505-Thr506, and Tyr560-Ser561. Cbfib2 cleaves mainly at Gly254-Ser255 and Pro516-Met517.