A study population of 240 young women who were sexual partners of men suffering from nongonococcal urethritis was investigated to establish whether it is possible, using routine cytology, to identify morphologic changed of diagnostic value in cervicitis due to Chlamydia trachomatis. Nonspecific severe inflammatory cellular atypias were significantly more frequent in the group of 93 C. trachomatis culture-positive women (38%) than in the control group of 147 C. trachomatis culture-negative women (18%). Tissue repair cells, appearing as a result of marked tissue destruction, were fond in 12% and in 3%, respectively. Intracytoplasmic inclusion bodies, pathognomonic of C. trachomatis, were not discovered in smears stained by papanicolaou's method. Hence, routine cytology is not the proper diagnostic method for chlamydial cervical infection. Dyskaryotic changes showing mild dysplasia occurred significantly more often in the C. trachomatis culture-positive women. This observation justifies the assumption that chlamydial infection may play a part in the development of dysplastic epithelial atypias of the cervix.