Flow cytometric measurements of the DNA content were performed in a prospective study of 167 women with invasive squamous cell carcinoma of the uterine cervix. Ploidy level and the proportion of S-phase cells were correlated to age, menopausal age, staging according to FIGO and histopathology. With increasing age a successive shift from a dominance of peri-diploid and peri-tetraploid values to marked aneuploidy was found. Peri-diploid and peri-tetraploid tumors were more often found in premenopausal than in post-menopausal women (p less than 0.001). The mean S-phase rate was significantly higher in women aged 60-89 years than in women aged 20-59 years (p less than 0.01). More aneuploid tumors were found in stages III and IV than in stages IB and II (p less than 0.01). The mean S-phase rate was higher in stages III and IV (20.8%) than in stages IB and II (17.2%) (p less than 0.01). No statistically significant correlation was shown between ploidy level and histopathology or between S-phase rate and histopathology. In 37 patients polyclonal tumors were found. The reproducibility of the method was good (r = 0.99).