In a chromosome study in childhood T-cell leukemia/lymphoma, we found t(7;11)(q35;p13) in 2 patients, t(7;14) (q35;q11) in one patient, and t(7;14)(p15;q32) in 1 patient. Southern blotting and in situ chromosomal hybridization studies in one patient with the t(7;11) demonstrated that both alleles of the T-cell antigen receptor beta-subunit gene (TCRB) were rearranged, and that one TCRB allele had relocated from 7q35 to the fusion point in band p13 of the involved chromosome 11 (11p-). These findings suggest that juxtaposition of TCRB with the putative oncogene tcl-2 located in band 11p13 may be a critical step toward development of this T-cell leukemia/lymphoma. In the other two translocations, all breakpoints were sites for lymphocyte function genes, ie, 7q35 for TCRB, 14q11 for T-cell antigen receptor alpha-subunit gene (TCRA), 7p15 for T-cell antigen receptor alpha-subunit gene (TCRG), and 14q32 for immunoglobulin heavy-chain gene (IGH). Thus, the findings in these cases allow us to expand the above hypothesis and propose that the juxtaposition of TCRB or TCRG with tcl-2, TCRA, or IGH through chromosomal translocation may activate a mechanism for the genesis of T-cell leukemia/lymphoma with these chromosome translocations.