A Sepharosyl-glycyltyrosyl-(N-(p-aminophenyl)oxamic acid) (Seph-Gly-Tyr-(NAPOA)) column was constructed in order to purify Clostridium perfringens sialidase (mucopolysaccharide N-acetyl neuraminylhydrolase, EC 18.104.22.168) by affinity chromatography (Cuatrecasas, P. and Illiano, G. (1971) Biochem. Biophys. Res. Commun. 44, 178-184). The results show that at pH 5.5 haemagglutinin, haemolysin and phospholipase C, as well as sialidase adsorb to the column. They do not adsorb to Sepharose 4B but will stick to Sepharosyl-glycyltyrosine at the same pH. The latter column appears to be acting as a cation exchange resin because at pH 7.5 this non-specific adsorption is largely overcome. When these proteins are applied to the affinity column at pH 7.5 only sialidase is adsorbed. It is not possible to say whether this is due to specific affinity chromatography or is still due to ion exchange effects. The results show that the method, as used here, is not suitable for the purification of C. perfringens sialidase because of this non-specific adsorption of other proteins.