Microscopic diagnosis of vaginal discharge established so far by means of microbial vaginal pictures (MVP) has proved to be insufficient. Phase contrast microscopy has an irreplaceable value in diagnosing vaginal infections transmitted by sexual intercourse. It yields quick and exact diagnosis of the disease, thus providing the possibility to administer treatment addressly and immediately. In equivocal findings and relapses vaginal cultivation is indispensable. In a series of 600 examined women vaginal trichomoniasis was diagnosed in 28.5% of cases. Simultaneous occurrence of other sexually transmitted diseases was recorded in 42% of 171 women infected with Trichomonas vaginalis. In these cases, the course of the disease was markedly altered by the associated infection. The result of MVP was incomplete or false in 26% of the examined women, trichomoniasis failed to be diagnosed in 80 cases.