Cytogenetic studies of non-Hodgkin's lymphomas (NHL) have revealed a nonrandom translocation, t(14;18)(q32;q21), to be strongly correlated with follicular histology. In our recent study of 149 cases of NHL, 68 cases had a t(14;18). Forty-four of these were follicular and 24 diffuse. In the majority of cases (90%) there were additional chromosome abnormalities, which were analyzed to determine whether any were specifically associated with diffuse histology. Chromosome 11 abnormalities occurring together with the t(14;18) were found to be present in 17/68 cases; 14/17 (82%) were diffuse and 3/17 (18%) were follicular NHL. Thus, 14/24 (58%) of all diffuse lymphomas with t(14;18) had an abnormality of chromosome 11 compared to only 3/44 (7%) of follicular lymphomas, suggesting that the addition of an abnormality of chromosome 11 to a t(14;18) karyotype is associated with diffuse histology.