Strain relatedness and switching were monitored in Candida albicans strains isolated from different body locations through three episodes of recurrent vulvovaginal candidiasis separated by two treatment-latency periods in a single patient. Strain relatedness was assessed by comparing Southern blot hybridization patterns with the relatively inimobile mid-repeat sequence Ca3. The following conclusions are demonstrated. (i) Three different strains of C. albicans colonized the mouth, the area under the breasts, and the vulvovaginal, anal, and rectal regions, respectively, at the tîme of the first infection. (ii) The same strain of C. albicans was responsible for the three vaginal infections. (iii) Switching of colony phenotype occurred with each new vaginal infection. (iv) Enrichment of drug-resistant switch phenotypes (assessed in vitro) was unlikely the basis for the changes in the switch phenotypes of the strain found in the vulvovaginal, anal, and rectül areas after treatment of the first infection with clotrimazole. (v) The same strain of C. albicans was responsible for the recurrent increases in mouth colonization and was distinct from the recurrent vaginal strain. The results of this case study demonstrate the need for further detailed analyses of full-body mycofloras, strain relatedness, switching repertoires, and changes in drug susceptibility during successive episodes of recurrent vulvovaginal candidiasis.