BCH-527, the lipophilic hydrochloride salt of octadecyl D-alanyl L-glutamine, was evaluated for efficacy against experimentally induced murine cytomegalovirus (MCMV), influenza A (H1N1) (IV-A), and Punta Toro virus (PTV) infections in mice. The compound was administered i.p. every other day for a total of 4 injections commencing 24 h previrus exposure. Doses ranged from 12.5 to 200 mg/kg per injection in the various experiments. The MCMV infection was significantly inhibited in two experiments by doses of 25-200 mg/kg, as manifested by increased numbers of survivors and decreased titers of virus recoverable from tissues. The IV-A infection was weakly inhibited, with antiviral activity seen in lowered lung scores and lung weights and less decline in arterial oxygen saturation values. The PTV infection was not inhibited. BCH-527 was stimulatory to cytotoxic T-cells, natural killer (NK) cells, macrophages, and splenic B-cells. The highest dose tested, 200 mg/kg, was inhibitory to cytotoxic T-cell activity and to some extent to NK cell and macrophage activity. These data suggest BCH-527 functions as an immune modulator in exerting the observed antiviral activity.