Seven patients with various adrenal processes (1 cortical hyperplasia, 6 adenomas, 1 cortical carcinoma, 1 malignant pheochromocytoma) have been examined using ultrasonic technique, computer-aided tomography, hormonal tests, and flow cytometry. The findings have been correlated to the results of cytologic and histologic studies. One of the aims of the study was to find out whether DNA content was a factor permitting the diagnosis of the adrenal tumor nature. A diploid distribution of the DNAs with a varying content of proliferating cells has been found in benign tumors of the adrenals, whereas the malignant tumors have been aneuploid with varying ratios of the diploid to aneuploid tumor cells. Study of the DNA content by flow cytometry helps assess the cell ploidy distribution in the studied population and their proliferative activity, thus permitting a more accurate morphologic characterization of the tumor and, possibly, giving more reliable diagnostic criteria.