Liver biopsies from ten patients with clinically mild or moderate acute virus hepatitis, taken in the acute phase of the disease and in the recovery phase or later, were assessed for the size of liver cell nuclei and the number of binuclear nuclei. A parametric model of the distributions of the nuclear radii was used to estimate the mean nuclear radius of diploid nuclei and the frequencies of di‐, tetra‐ and octaploid nuclei. During the acute phase of virus hepatitis the liver cell nuclei were often larger, with greater variation in size, than in the recovery phase. This pleomorphism was not only due to pyknotic and necrotic nuclei as these were not measured. It is assumed that the enlargement of the nuclei was due to increased metabolic activity of the nuclei. The frequencies of polyploid nuclei and binuclear liver cells were higher in the first biopsies, probably reflecting regenerative activity. No correlation was found between the severity of the disease as judged by liver histology or routine liver tests and the degree of nuclear changes with respect to size and frequency of polyploid or binuclear liver cells.