Experimental studies of arbidol and arbidol mesylate versus ribavirin suggest that insertion of these agents into the nutrient medium of the cultured cells GMK-AH-1 (D) after infection at concentrations of 50, 25, and 100 microg/ml, respectively, is effective in suppressing the reproduction of severe acute respiratory syndrome (SARS) virus. Arbidol and arbidol mesylate were shown to have a direct antiviral effect in early viral replication in the cultured cells. The promising antiviral agent is arbidol mesylate that is nearly 5 times as effective as arbidol in reducing the reproduction of SARS virus in the cultured cells. Insertion of arbidol, arbidol mesylate, and ribavirin into the nutrient medium 2 hours after infection of porcine embryonic renal cells caused a reduction in the accumulation of the pathogen by 2.5, 2.1, and 2.6 Ig, respectively.