The nature of TCR gamma and delta gene rearrangements in 4- to 6-week-old scid thymocytes was examined by using the polymerase chain reaction technique, cloning, and DNA sequencing. Analysis of 78 sequences indicates that TCR gamma and delta gene rearrangements in scid mice generally resemble those in thymocytes from normal young adult mice. V gamma 1, V gamma 2, and V gamma 5 rearrangements are heterogeneous, with extensive N region addition and nucleotide excision from the recombining coding segments. In addition, homogeneous and fetal-like V gamma 3, V gamma 4, and V delta 1 rearrangements are observed. These rearrangements are currently difficult to interpret but may be significant with respect to whether certain homogeneous joints in normal mice are due to cellular selection or to the rearrangement process. scid TCR gamma and delta gene nucleotide sequences also reveal direct V-J delta joining, inter-(V-J-C gamma) cluster joining, and the possibility of inversional rearrangement at the gamma locus. Short sequence homologies may contribute to V(D)J recombination and to the rescue of blocked coding joints.