The non-proteinogen aminoacid mimosine interfered seriously with cultured carp hepatocytes when added to the culture medium for 6 h in a concentration of 0.1 M. Cell transformation started with condensation of the chromatin into an unusual network of fibrils and segregation of the reticulate nucleolus into its fibrillar and granular components. Then chromatin condensation spread homogeneously across the entire nucleus. At the end of the condensation period the nuclear envelope extended towards the cytoplasm and the nuclear interior resulting in a very confusing nuclear boundary. Later, the nucleus expanded and the chromatin was gradually decondensed but the segregated nucleolus persisted until nuclear lysis. The DNA staining pattern did not change throughout the condensation period. DNA was even present in most decondensing nuclei. The cytoplasmic organelles were only slightly affected during chromatin condensation but significantly altered thereafter. The observed course of mimosine-induced cell transformation is very unusual. The first period covering chromatin condensation with structural intactness of the cell organelles resembles in some aspects apoptosis but additionally includes some special signs. The following phase of cellular disintegration, however, is similar to necrosis. Due to this unique course of cell death, mimosine should be further tested for its potential suitability in experimental cell research and cancer chemotherapy.