To observe the composition of the vaginal flora of healthy women over time, and in relation to hormonal changes, sexual activity, and hygiene habits. A longitudinal surveillance of the vaginal flora over an eight week period. 26 female health care workers in local genitourinary medicine clinics. The participants were anonymised. They filled in diary cards daily. Blind vaginal swabs were self-taken two-seven times weekly. A smear was air-dried for later Gram staining. The swabs were also cultured for Candida spp, Gardnerella vaginalis, anaerobes, Mycoplasma hominis and Ureaplasma urealyticum. Of 26 subjects, only four had normal vaginal microbiology throughout. One woman, who was not sexually active, had bacterial vaginosis (BV) throughout and nine (35%) had intermittent BV. Candidiasis was found intermittently in eight women (31%), and eight had normal microscopy. U urealyticum was isolated intermittently in 40% of women with BV, 25% with candida, and 50% with normal microscopy. Many women were symptomatic, but symptoms correlated poorly with microbiological findings. All but two women were sexually active; however, more women with BV were exposed to semen. BV seemed to be related to frequent use of scented soap, and there appeared to be an additive effect of clothing and hygiene factors. Our study raises doubts about what should be regarded as normal vaginal flora. It calls into question the significance of finding BV or U urealyticum on a single occasion in asymptomatic women, or of finding normal flora in symptomatic women. The effect of external factors on the vaginal flora deserve further study.