When designing, developing, and testing pharmaceutical compounds, scientists rely on available data about the environmental pH of the target organ--in this case, the vaginal tract--for determining maximum absorption. In this study, we compared two commercially available pH papers with a handheld digital pH meter to assess their viability as methods for measuring vaginal pH in cynomolgus monkeys. We sedated 17 female cynomolgus monkeys (Macaca fascicularis) and measured their vaginal pH by using the three described devices. The results were comparable, and there were no significant difference among the three methods used; however, the color and consistency of the vaginal fluid and the visual acuity of the user did not affect the results measured using the handheld digital pH meter. We conclude that the handheld digital pH meter is a viable method for measuring vaginal pH in cynomolgus monkeys. Copyright 2004 American Association for Laboratory Animal Science