The nuclear morphology of preneoplastic and unaltered hepatocytes in diethylnitrosamine-treated rats was investigated. Two-micrometer-thick sections of methacrylate-embedded liver were scanned with a TV camera and evaluated in a computer using multivariate analysis methods. The preneoplastic cell populations (islands) were distinguished from unaltered hepatocytes by histochemical demonstration of glycogen storage in specimens from starved animals. After the hemalaun-stained liver sections were scanned randomly, the sections were stained for glycogen, and the previously registered cells were identified visually using a scanning stage for relocation. This objective identification of unaltered and preneoplastic hepatocytes formed the basis for the selection of a training set for feature evaluation and supervised classification. Image analysis for quantitative nuclear morphology was applied to the hemalaun-stained cells. The results showed that condensed chromatin was reduced and nuclear area was increased in the nuclei of glycogen-storing cells. Differences in the nuclear structure were also found. A multivariate analysis including seven features gave a correct classification result of about 82%.