Cytomorphology and immunocytochemistry were used to diagnose two cases of large cell anaplastic lymphomas that expressed the Ki-1 antigen. Smears stained with the May-Grünwald-Giemsa stain showed a cytomorphologic spectrum that varied from immunoblastlike cells to large tumor cells with pleomorphic nuclei. The tumor cells had a distinct basophilic cytoplasm, which often contained vacuoles. Giant cells with wreathlike multilobulated bizarre nuclei were also observed. Immunocytochemistry on a cytocentrifuged specimen showed that the tumor cells were of a T-helper phenotype; all strongly expressed the Ki-1 antigen and receptors for HLA-DR and IL-2.