The objective of this study was to determine the relative sensitivity of detecting Trichomonas vaginalis in endocervical as compared to ectocervical Papanicolaou-stained smears. The average number of organisms in 10 (200x) high-power fields (hpf) per smear was used for comparing the presence of trichomonads in the two smear types. In every pair of ectocervical-endocervical smears, there were always more trichomonads in the ectocervical smear. Fifty percent of cases showed at least 25 more trichomonads per 200x hpf in the ectocervical smear than in the endocervical smear. In 20 of 50 cases (40%), trichomonads were present only in the ectocervical smear. The organisms were found only in the endocervical smears of women with a heavier ectocervical trichomonad burden. In conclusion, trichomonads are detected in the Papanicolaou-stained ectocervical smear more often than in the endocervical smear; therefore, examination of an adequate ectocervical smear has greater utility than the endocervical smear for the diagnosis of trichomoniasis.