A high frequency (greater than 80%) of acute lymphoblastic leukemias (ALL) exhibit a recombination of the T-cell receptor (TCR) delta chain locus. Interestingly, distinct TCR delta elements are preferentially used in immunologic subtypes. In a recent series of 201 children with common ALL (cALL) we observed a TCR delta rearrangement in 162 patients, 57% of the latter showing a hybridization pattern in Southern blots suggestive of a V delta 2 to D delta 3 recombination. To verify this interpretation and to elucidate in more detail the diversity of this common type of TCR delta recombination we amplified and sequenced the junctional region of nine cALL patients and cell line REH-6 by polymerase chain reaction (PCR). A V delta 2 D delta 3 recombination was confirmed in all cases; convincing evidence for the participation of D delta 1 or D delta 2 elements was not obtained. Eight of nine patients and REH-6 showed complete 5' D delta 3 boundaries within V delta 2 D delta 3 segments, a limitation of junctional diversity also detected in 50% of peripheral blood cell clones derived from two healthy probands. Notably, sequence identity at the V delta 2 D delta 3 junction was demonstrated for a cALL and one of the control clones. Another group of 35 of 162 cALL patients was characterized by V delta 2 rearrangements and biallelic deletion of J delta and C delta sequences. Using a J alpha consensus primer, PCR-directed sequence analysis demonstrated V delta 2 D delta 3 J alpha recombinations in all four cases analyzed by this approach. The J alpha segments of these patients differed, but were identical or homologous to published J alpha elements. Our data suggest a recombination pathway of the TCR delta/alpha locus leading to chimeric TCR alpha molecules, containing V delta and, remarkably, also D delta sequences.