Detailed cytophotometric analyses of cell nuclear DNA content were performed on 132 different areas from 24 oesophageal squamous cell carcinomas with an intraepithelial component. Measurements of DNA content were performed at the three different areas within each of the intraepithelial and invasive components. There were no differences in the overall incidence of DNA distribution patterns which were classified according to the degree of dispersion and the peak value on the DNA histogram between intraepithelial and invasive components, as well as the average of mean values of the DNA content. In 13 (54%) of 24 cases, there was a variation among the DNA distribution patterns obtained from three different areas of the intraepithelial components, whereas there was a variation in 4 (22%) of the 18 invasive components. In 11 of 13 intraepithelial components with a variation, the same DNA distribution pattern as seen in the invasive component was present. Provided that the DNA content remains stable, variations in intraepithelial components may reflect various tumour cell populations. These findings support the idea of a multicentric carcinogenesis of oesophageal carcinoma, and shed light on the mechanisms in which a single cell population is selected from various cell populations in the progression from an intraepithelial to an invasive lesion.