OBJECTIVE The objective of the study is to determine the optimum diagnostics of vaginal yeast infections and to compare the effects of treatment of these infections by Natamycin with those by Clotrimazol. METHODS Prospective comparison of both option of treatment of vaginal infections. NAME AND PLACE OF RESEARCH: Obstetrics and gynaecology department, Brno-Bohunice. METHODS 30 patients treated with hydrophobe Natamycin and 20 patients treated with hydrophyll Clotrimazol formed a sample of 50 women. Regular checks were made on the 10th and 30th day after the beginning of treatment. Diagnosis was performed by means of native microscopy supplemented by an examination for cultivated yeasts in the culture medium "FUNGI-QUICK". At the same time a microscopic examination of slides stained by Gram and Giems was made. RESULTS A correlation between the evaluated native slide and the culture examined thereafter was 96%. Statistical evaluation of the difference of the rate of success of treatment between the two groups by means of the t-test revealed a value of 0.29, the level of probability was 0.05 at N1 = 0.1795 and N2 = 0.2179. CONCLUSIONS Native microscopy is irreplaceable in the diagnosis of vaginal candidosis. No significant differences in the effects of treatment with Natamycin and Clotrimazol were found. On the basis of these results we made some recommendations on the principles of optimum treatment.