DNA ploidy assessments of 72 archival paraffin embedded specimens were made utilizing flow cytometry (FCM) and image cytometry (ICM). Forty four specimens were obtained from primary prostatic tumours and 28 from metastatic lymph nodes. Eighteen of 30 FCM diploid range tumours were aneuploid by ICM. Nineteen of 22 FCM tetraploid range tumours were ICM aneuploid. All FCM non-diploid range specimens were non-diploid range by ICM, and all ICM diploid range specimens were diploid range by FCM. ICM more easily identifies small numbers of aneuploid cells than FCM. Discrepancy between FCM and ICM measurements was particularly high in lymph node specimens. FCM diploid range distributions mostly occurred in lymph nodes with a small tumour fraction whereas the number of aneuploidy specimens increased with larger tumour volume. Lymphocytes are different from solid tumour cells since they are not fixed in tissue and will probably be more easily dissolved in cell suspension when sections are disintegrated. This may influence FCM measurements and has to be considered when DNA ploidy measurements of lymph node metastases are made.