We analyzed the morphonuclear features of thyroid cell nuclei from 10 normal tissues (10 multinodular goiters), 10 benign tissues (10 adenomas) and 10 neoplastic tissues (10 carcinomas--2 follicular, 2 medullary and 6 papillary). These morphonuclear features quantitatively described the nuclear size, DNA content and chromatin texture of 200-400 Feulgen-stained cell nuclei that were digitized by means of a cell image processor. Nuclear DNA estimations revealed that the benign thyroid tumors showed an aneuploidy level that was not different from that of the neoplastic tissues. Morphometric measurements showed a significant and positive correlation between an increase in nuclear area and the development of thyroid pathology--i.e., from normal to a neoplastic stage. We also observed a significant decrease in chromatin condensation and heterogeneity from normal to neoplastic thyroid tissue. In the specific case of thyroid tumors, such criteria were not found sufficient per se for a diagnosis of malignancy. More detailed data banks will be necessary for this purpose.