The sera of 263 women--217 infertile and 46 pregnant--were examined by various serological methods (precipitation test, agglutination, indirect immunofluorescence) to detect Candida guilliermondii var. guilliermondii (C.g.) infection. The precipitation reaction was performed with extracellular C. guilliermondii antigen, the agglutination reaction was employed parallel with C. albicans. In the infertile group 122 (56.2%) proved to be C.g. positive, while in the fertile 11 women (23.9%) proved to be so, the level of significance being p less than 0.0001 between the two groups. A one-month ketoconazole treatment (one tablet, 200 mg/day) was adequate for eliminating the C.g. infection. In a few cases hystological examinations were also performed according to Gomori-Grocott and yeast cells could be detected in the stroma of the ovary. IgA, IgG, IgM, Gc-globulin, transferrin and ferritin determinations were carried out before and after the ketoconazole treatment, and there were significant differences in the IgM and transferrin levels between the infected and non-infected groups. The authors achieved 5 pregnancies of 56 treated women in 6 months.