The effect of zinc salts and complexes were evaluated on the replication of rhinovirus 2 in vitro. Zinc chloride inhibited the replication of rhinovirus 2 at concentrations between 3 and 12 micrograms/ml. Influenza virus was not affected. A number of zinc complexes were tested and compared to zinc chloride. The results indicated that the activity and toxicity of all zinc complexes in the rhinovirus cytopathogenic effect (CPE) assay were directly related to the amount of unbound zinc available.