The adherence to vaginal epithelial and uroepithelial cells of three serogroups (W/I, W/II and W/III) and their colony colour opacity variants of Neisseriagonorrhoeae were studied with regard to the menstrual cycle, using an in vitro test method. Vaginal epithelial cells obtained in the post-menstrual phase attach more gonococci than cells obtained in the premenstrual phase. This difference was statistically highly significant (p < 0.001) for the three serogroups tested. The adherence rate also differed with regard to the three serogroups used in the tests (W/II > W/III > W/I), and with regard to organisms from opaque or transparent colonies (opaque > transparent). There was no variation in the adherence of gonococci to uroepithelial cells during the menstrual cycle. E. coli, S. saprophyticus and group B streptococci showed a tendency to increased adherence to vaginal epithelial cells in the post-menstrual phase compared with the pre-menstrual one, but the difference was not statistically significant.