The DNA content of paraffin-embedded materials was determined retrospectively using flow cytometry (FCM) in 36 germ cell tumors, and related to histological type, clinical staging and tumor marker. These histograms were classified from the basis of mode and variance into a diploid and an aneuploid pattern. We could evaluate the DNA histograms in 20 of 36 specimens (56%). Aneuploid patterns were found in 11 of 20 evaluated cases, but there was no correlation between ploidy patterns and histological types. Aneuploid patterns were demonstrated in 2 of 6 stage I cases (33%), and 4 of 5 stage II cases (80%) in seminomas. The difference between stage I and II cases was not statistically significant. There was no correlation between clinical staging and DNA content in non-seminomas. Of the seminomas with elevated human chorionic gonadotropin (HCG) titers, 3 of 4 cases showed aneuploid patterns. These findings indicate that the determination of DNA ploidy in seminomas may prove to be of prognostic value.