A simple, rapid and quantitative protein A binding radioimmunoassay (RIA) was developed to screen and evaluate antiviral drugs against human cytomegalovirus (HCMV) replication. It was found that (S)-1-[(3-hydroxy-2-phosphonylmethoxy)propyl]cytosine (HPMPC) and human gamma-interferon (IFN) were more effective than 9-[(1-3-dihydroxy-2-pro-poxy) methyl]guanine (DHPG) and other IFNs against HCMV replication in human fibroblast cells. The block in virus replication was not due to toxic effect of these compounds on human fibroblast cells. The results were in good agreement with those of other workers. The results indicate that protein A binding RIA can be useful for rapid and quantitative screening of compounds effective against HCMV replication. © 1994.