Dichloroflavan was found to stabilize rhinovirus 1B to inactivation by heat at 56 degrees C or by acid at pH 4.6 to 5.0. The effects of dichloroflavan, arildone and sodium dodecyl sulphate on uncoating of virus in M.HeLa cells were compared by examining the production of sub-viral particles separated on sucrose density gradients; the development of photoresistance by neutral red labelled virus. All three compounds significantly reduced but did not completely suppress the production of sub-viral particles. They also affected the uncoating of neutral red labelled virus, although dichloroflavan appeared to delay rather than prevent this process. A variant of rhinovirus 1B, isolated by growth in the presence of dichloroflavan, showed increased resistance to inhibition by arildone and SDS as well as dichloroflavan, suggesting a similar site of action for the three compounds.