The determination of DNA ploidy and the study of the cell cycle in adrenocortical tumoral cells could help in the distinction between benign and malignant lesions and also in the prediction of the biological behaviour of these tumors. We analysed 32 cases of adrenal tissue (8 normal adrenals--N, 12 benign adenomas--A and 12 carcinomas--C). DNA was quantified by image analysis of Feulgen stained sections (Ahrens System) employing ACAS3 software. The DNA content was considered to be diploid in 70% of the N and in 67% of the A groups and in none of C. In this latter group nearly 90% were triploid or tetraploid while this did not occur in any of the A cases. The percentage of cases with a 5c-exceeding rate (5cER) above 5% was nil in the N and A groups and 100% in C. In what concerns the distribution in the cell cycle we found a very distinctive pattern between the groups as the percentage of cases in which the S-phase fraction exceeded 33% was nil in the normals, 8% in A and 83% in the C cases. In conclusion, there was a good correlation between the analysed parameters and the clinically defined groups of adrenal cortex tumors.