The surface pH of the vagina was measured before and after sexual arousal by self-stimulation in ten healthy women. The mean value of six spots measured and pH measured in collected vaginal fluid was highly correlated. Two-way analysis of variance showed a mean increase of pH after orgasm (significant at the 0.5% level). The Wilcoxon matched-pairs test and a paired t-test showed a significant increase in three and four of the subjects, respectively, and a decrease in pH in one other subject. It is concluded that in the present laboratory setting, clitoral self-stimulation to orgasm only results in small changes of the vaginal surface pH.