Abstract: Hyaluronidases (hyalases) from bovine testes and leeches were used as "standard". Constituents of crude snake venoms-hyalases were separated by size exclusion HPLC. Molecular masses of hyalases from snake venoms, determined by on-line capillary HPLC-mass spectrometry with electrospray ionization, were: Naja melanoleuca (black cobra) 49377Da, Naja Kaothia(Thai cobra)60265Da, Sepedon hemachatus (ringhals cobra) 49722Da. Mass determinations were repeatable within 0.03%.