We have considered the cytogenetic abnormalities present in 27 unpublished cases of B-immunoblastic lymphoma. Among these 27 patients, the chromosome changes were heterogeneous and complex. The chromosomes most commonly gained were 3 (44% of cases), 18 (44%), 6 (30%) and 11 (30%). The most common structural abnormalities involved band 14q32 (26%), band 18q21 (15%) and bands 6q16-21 (19%). Study of these 27 immunoblastic lymphomas did not allow us to tentatively identify a common primary cytogenetic abnormality unique to B-immunoblastic lymphoma, however, a translocation at 14q32 may be the primary cytogenetic lesion in some of the cases. Rather, we have added to the number of abnormalities reported in immunoblastic lymphoma and in non-Hodgkin's lymphoma in general.