Fine needle biopsies from 70 patients with prostate carcinoma and 10 patients with benign hyperplasia were used to study area, variation in size and form factors of the nuclei by image analysis. The results were related to DNA ploidy of the cell populations as measured by flow cytometry, cytologic grade and patients' survival. Nuclear area differed significantly between benign lesions and tumors. It increased in diploid low-grade tumors from a normal value of 54.2+/-3.1 microns2 to 75.6+/-5.3 microns2. In aneuploid tumors with an increase in the chromosome number, the nuclear size further increased to about twice that of benign nuclei. Variation in size also differed between benign and malignant epithelium, with a further increase between diploid and gross aneuploid tumors. While nuclear size and variation in nuclear size made it possible to discriminate malignant from benign lesions, form factor did not differ between benign and malignant lesions. In follow-up, however, none of these factors reached significance for predicting survival.