The three components of virus-induced interferon (IFN) from C243 cells, with molecular weights of 19,000, 24,000 and 30,000, were examined for neutralization by antisera against the alpha (24,000) and beta (36,000) types of virus-induced L cell IFN. The results indicated that the C243 19,000 component belongs to the alpha type, and the 24,000 and 30,000 components to the beta type. The 19,000 component was also indistinguishable from L cell IFN-alpha in the reaction with antisera against human IFN-alpha.