Circular DNA excised mostly by gene rearrangements was isolated from adult thymocytes and splenocytes and cloned into a bacteriophage vector. Analysis of DNA clones showed the lower frequency of T cell receptor (TCR) δ locus compared with the flanking α locus. This suggests that TCR δ locus is successively rearranged from the inside and the excision products are progressively diluted out by the following cell multiplication entailing α gene rearrangements. New V δ subfamilies, special usage of J δ 2, reciprocal joining of two D δ elements and novel sequences homologous to the human δ-gene deleting elements were also found.