After treatment with neuraminidase, human leukocyte interferon (HLI) retained its characteristic heterogeneity when subjected to isoelectric focusing. The clearance of HLI from the circulation of rabbits, injected intravenously, was unaffected by treatment with neuraminidase or subsequent treatment with galactose oxidase. Complementary chemical treatments were similarly without effect. None of the treatments resulted in destruction of biological activity. Sialic acid and galactose or its derivatives do not appear to contribute to either the antiviral activity or the pharmaco-kinetics of HLI.