Quantitative cultures of the vaginal introitus for Enterobacteriaceae, S. faecalis and P. aeruginosa were compared in 20 premenopausal normal women (200 cultures) to 198 consecutive cultures from 9 premenopausal women in between episodes of bacteriuria. Introital colonization in patients susceptible to urinary infections was significantly higher for E. coli (p equals 0.001), S. faecalis (p equals 0.001) and for the presence of any gram-negative pathogens (p equals less than 0.001). In addition, introital colonization with these bacteria occurred in larger numbers and persisted through consecutive cultures for longer periods in women with recurrent infections.