We have correlated immunological characteristics and karyotypic abnormalities from lymphomas in 118 patients. T-lymphomas differed significantly from B- and non-B-, non-T-lymphomas in having more normal metaphases, trisomy 19, and breaks at 1q21, 2q21, 3q27, 4q21, and 17q21 (P less than or equal to 0.03). Non-T-lymphomas had breaks in 18q in one-half the cases, but only one of 11 T-lymphomas had such breaks (P = 0.02). Among B-lymphomas, specific chromosome abnormalities were associated with the type of immunoglobulin heavy but not light chain expressed. A break at 14q22 or q24 was associated with surface delta mu-immunoglobulin (P = 0.02); trisomy 22 or a break in 22q and a break at 2q32 was associated with surface gamma-immunoglobulin (P less than 0.001); and trisomy 12 and a break at 2p13 was associated with cytoplasmic gamma-immunoglobulin (P less than 0.01). Among B-lymphomas, several cytogenetic abnormalities were associated (P less than or equal to 0.02) with expression of CD24 or CD9 surface antigens. Lack of CD24 was associated with breaks in 2p25, 5q, and 6q21; CD9 was associated with a break at 6q15. Associations with a specific immunological phenotype were not identified for cytogenetic abnormalities involving a band to which genes encoding immunoglobulin or the T-cell receptor have been localized. Breaks were common at 14q32, the genomic site of the immunoglobulin heavy chain loci, in B-, non-B-, non-T-, and T-lymphomas. In T-lymphomas this may be because this is the site of the AKT1 oncogene. Breaks were uncommonly found at the light chain loci or the genomic sites encoding the T-cell receptor. However, the recurring breakpoints associated with T-lymphomas were commonly found on chromosomes to which genes coding for various T-cell antigens have recently been provisionally assigned.