Studies of lymphoproliferative disorders using immunoglobulin and T- cell receptor genes have contributed to our understanding of clonality and lineages of these disorders. In this study, we examined the rearrangement of the recently discovered T-cell delta chain genes in a variety of lymphoproliferative diseases. We show here that six of 14 T- cell lymphomas and five of 23 B-cell lymphomas or B-cell leukemia cell lines have rearranged the delta loci, while two of two hyperimmune reactions retain germline configuration within these genes. Seven of ten cases of AILD were rearranged, and Lennert's lymphoma, which has been previously described as a T-cell malignancy, also contains rearrangements in the delta chain genes (three of five). Large cell anaplastic lymphomas positive for the activation antigen CD 30 also contain rearrangement in about one-half (five of 11) of the tumors examined. Two of seven of the Hodgkin's lymphomas studied contained a rearrangement for this gene. This study indicates that this newly identified T-cell delta gene is useful in evaluating clonality but is not lineage specific. However, with only one exception (in 28 rearrangements), this gene rearranges in tumors with gamma and beta chain gene rearrangements, indicating that when used in conjunction with the other TcR genes, delta rearrangement may also be useful in evaluating lineages.