Biopsies of nasal epithelium consisting of metaplasia (stratified cuboid epithelium, mixed stratified cuboid/stratified squamous epithelium and squamous epithelium), dysplasia and carcinoma, were the subjects of morphometric analysis using semithin sections of plastic embedded material. Use of a semiautomatic device for image analysis (MOP, AMO3, Kontron) facilitated the workload considerably but not at the expense of reliability. The measurements were restricted to the basal layer. The preliminary study consists of scanning and transmission electron microscopy besides morphometry. The most interesting electron microscopic finding was a significant reduction in foldings of the surface of the plasma membrane in dysplasia with a nearly complete loss in carcinoma and an increase of desmosomes in dysplasia. The most conspicuous light microscopic finding was an increase in the cell size with largest values in dysplasia (162 +/- 16 micrometer 2) and an unchanged nuclear/cytoplasmic ratio for the different types of metaplasia of 0.28 in contrast to dysplasia and carcinoma of 0.31 and 0.51 respectively. Alterations of the karyoplasm consisted of a conspicuous, gradual increase in the percentage of nuclei containing nucleoli, which was nearly 100% in carcinoma. The nucleoli fraction per nuclei was 7.6% in dysplasia, which was a 2 or 1.5 times increase compared to stratified cuboid epithelium or carcinoma respectively. This increase was mainly the consequence of an enlargement of the average nucleoli size which was 2 or 3 times higher in atypia (9.3 +/- 1.4 micrometer 2) than in stratified cuboid epithelium and carcinoma respectively. Further work is in progress to enlarge the number of analyzed cases and especially to quantify the ultrastructural alterations.