A series of derivatives of dibenzofuran and dibenzosuberol block rhinovirus replication in vitro as judged by their ability to hinder the cytopathic effect in cells infected with HRV14 or HRV16. Both the number and the size of viral plaques were reduced effectively by treatment with these compounds in a dose-dependent fashion, thus affecting viral spread. The compound 2-hydroxy-3-dibenzofuran carboxylic acid was equally effective against HRV16 and HRV14, with IC50 values of 25 microM in cytopathy assays. Dibenzosuberenone showed minor differences in selectivity, with IC50 values of 10 and 30 microM for HRV16 and HRV14 cytopathy, respectively. Likewise, dibenzosuberenone effectively prevented the production of HRV16 proteins, viral RNA, and infectious virus particles when present at concentrations above 30 microM. Time-of-addition experiments show that compounds must be administered before or during the viral adsorption step in order to be effective antivirals. Dibenzosuberenone can block the adsorption of viral particles on to cells, preventing further steps in the replication cycle, but is not effective as a direct inactivating agent. These compounds likely interact with viral capsid proteins, affecting receptor interactions required for attachment and subsequent entry into cells.