Adherence of Escherichia coli to human uroepithelial cells obtained from the midstream urine of healthy women, nd to vaginal and buccal cells obtained from 11 healthy women and 24 patients who had had at least three urinary tract infections in the preceding year was studied. Bacteria labeled with [3H] uridine were used, and unattached organisms were separated from the epithelial cells by vacuum filtration through a polycarbonate membrane filter (5-micrometers-pore-size). A day-to-day variation in the receptivity of uroepithelial cells was noted. The range and rapidity of change in adherence to both vaginal and buccal cells were greater in patients than in controls. Adherence to vaginal cells was greater in patients than in controls (10.1 +/- 0.92 vs. 3.8 +/- 0.47 bacteria per cell [mean +/- S. E.], P less than 0.001), as was adherence to buccal cells (1.7 +/- 1.29 vs. 7.1 +/- 0.49, P = 0.002). There was a very strong, positive non-linear correlation between vaginal and buccal cell receptivity (R = 0.87, P less than 0.0001). The data suggest that susceptibility in women to urinary-tract infections is associated with widespread, fluctuating changes in the adhesive characteristics of epithelial cells.