In a series of 2,346 Papanicolaou-stained smears from women undergoing routine gynaecological examination, 39 showed cytomorphological signs of inflammation suggesting Chlamydia trachomatis infection (Papanicolaou class II or III). The 39 smears were studied microbiologically by the direct-immunofluorescence test and cell culture to see whether chlamydial infection correlated with the presence of Mycoplasma hominis and Ureaplasma urealyticum. The results were compared with the cytological and colposcopic findings. C. trachomatis was cultured in 56.41% of the 39 smears, and isolated by the direct-immunofluorescence test in 51.28%. M. hominis was detected in 35.89% and U. urealyticum in 25.54%. Though all three organisms coexisted in 10.25% of the smears, C. trachomatis and M. hominis in 15.38%, C. trachomatis and U. urealyticum in 2.56%, no valid conclusions could be drawn from their association. The study did, however, indicate that vacuolated cells and cells with "bubbly" cytoplasm are common also to other infections seen in PAP-test smears and do not necessarily warrant a diagnosis of C. trachomatis, but that Gupta-type intracellular inclusion bodies do.