The clinical histopathological and immunophenotypic features in 5 patients with Ki-1 positive non- Hodgkin's lymphoma (NHL) were studied. When first seen, 4 patients presented enlargement of superficial lymph nodes, with skin lesions in 2 patients. Two patients in stage IV with fever, hepato-splenomegaly and bone marrow invasion, died. Histologically, the tumor cells showed diffused or patchy hyperplasia. The cells were relatively large in size, rich in basophilic or slightly eosinophilic cytoplasm with irregular-shaped nuclei, prominent nucleoli, and distinct anaplasia and pleomorphism. Some of the cells looked very much like the Reed-Sternberg cells. Multinucleated giant cells were seen. Immunophenotypieally, all the cells were CD30 (Ki-1) and CD25 (IL-2 receptor) positive but CDI5 (Len M1) negative. Thus, the 5 patients with Ki-I positive NHL were all of T cell type.