The nuclear area, N/C ratio and anisonucleosis by morphometry and the DNA content by image photo-cytometry of paraffin-embedded tissues of 9 cases of prostatic hypertrophy and 48 cases of carcinoma obtained by open surgery, needle biopsy or by autopsy were correlated with histological grading. In histological grading, in addition to 9 benign hypertrophy cases, 11 were classified as well differentiated adenocarcinoma, 19 as poorly differentiated adenocarcinoma and 1 as small cell carcinoma. All 14 tumors taken from distant metastasis were classified as poorly differentiated adenocarcinoma. Correlation of the data by tumor cell morphometry with those of nuclear image photo-cytometry was carried out on surgical materials alone. In autopsy materials, DNA ploidy patterns were compared between primary lesions and metastases. The DNA histogram patterns of most cases were classified into 4 groups. Hypertrophy was differentiated from carcinoma by the histogram patterns. There were significant correlations between mean DNA value and morphometric factors. One of the 4 histogram patterns had a higher mortality than others. The DNA histograms did not distinguish between the primary and metastatic lesions of the same patients. However, the DNA histograms constructed from metastasis frequently showed a single stem-line of the primary lesion. This study disclosed several correlations between histological grading and morphometrical factors.