Thrombin-like activities were not observed inCrotalus basiliscus, C. molossus and C. scutulatus scutulatus crude venoms. 5\u27-Nucleotidase specific activities of 0.863, 0.273 and 5.520 units/mg of crude venom protein were observed inC. basiliscus, C. molossus and C. s. scutulatus venoms, respectively. Concanavalin ASepharose 4 B (Con A)affinitychromatography yielded two fractions from each of the crude venoms. Ineach instance, both fractions exhibited 5\u27-nucleotidase activities and the Con A-binding proteins had higher activities than the Con A-nonbinding proteins. 5\u27-Nucleotidase activities inthe DEAESephadex A-50 chromatographic fractions were localized in the first elution fraction and the last fraction(s) to elute. EDTAhad no effect on the 5\u27-nucleotidase activities ofthe crude venoms