In 7 female volunteers the local vaginal blood flow was calculated from the washout of the radioactive inert gas xenon 133 after an intraepithelial injection. During rest a monoexponential washout curve was found for the whole washout process. The average vaginal blood flow (VBF) was found to be 9.8 ml.min-1. (100 g)-1 (range, 5.5 to 19.6). In 6 of the women when sexual stimulation was undertaken an increase in blood flow was recorded to an average of 28.9 ml.min-1. (100 g)-1 (range, 21.5 to 45.0).