We investigated the significance of HPV 16, 18 infection and DNA ploidy in the progression to malignancy of uterine cervical dysplasia. Formalin-fixed, paraffin-embedded surgical and biopsy specimens obtained from 59 women were examined. The 59 women were classified into two groups: one of progression cases and the other regression cases. Polymerase chain reaction (PCR) and dot blot hybridization (DBH) were used for the detection of HPV 16/18 DNA, while flow cytometry was used for the analysis of the relative cellular DNA content in samples prepared by Hedley's method. Eight out of 29 progression cases (27.6%) and 3 out of 30 regression cases (10.0%) exhibited HPV 16/18 DNA, whereas 14 out of 29 progression cases (48.3%) and 2 out of 30 regression cases (6.7%) involved a DNA aneuploid population, representing a DNA index in the former above 1.5 and in the latter below 1.5. The proportion of cases having a population of DNA aneuploid together with the presence of HPV 16/18 DNA was 20.7% (6/29) in the progression group and 0% (0/30) in the regression group. These results indicate that the DNA aneuploid population coupled with simultaneous HPV 16, 18 infection may be used as a marker for progression in uterine cervical dysplasia.