The activity of cephradine and the influence of pH on its activity against 70 Gardnerella vaginalis strains were determined. Serial dilutions of cephradine (0.062 to 256 gug/ml) were incorporated into Dunkelberg agar, inoculated with a Steers replicator, incubated in 5% CO2 for 48 h, and examined. The minimal inhibitory concentrations for 90% of the isolates were 16 and 8.0 ,ug/ml at pH 7.0 to 6.0 and 5.5, respectively.