Chromosome abnormalities of three patients with Ki-1 lymphoma are presented. In order to be included in the study each case fulfilled the following criteria: the majority of the tumour cells were positive for the Ki-1 antigen (CD30), and the cells were large with relatively abundant, slightly basophilic cytoplasm. In all cases, a major proportion of mitoses contained a complicated clonal chromosome abnormality. Two patients had a 2;5 translocation; and the third had break points at 14q32 and 2p12. The latter patient showed expression of B-cell antigens and had rearrangements in the immunoglobulin heavy chain and kappa light chain genes. The two patients with the 2;5 translocation were epithelial membrane antigen positive, but did not exhibit rearrangements of immunoglobulin/T-cell receptor genes or expression of T-/B-cell antigens.