The earliest TCR+ cells to appear during fetal development express products of the gamma and delta loci, and emerge as successive waves of cells bearing different V gamma gene products. These appear to emigrate and seed different epithelia. The TCR repertoire of the first two of these waves, V gamma 3 and V gamma 4, respectively, is extremely restricted. Whether the repertoire of these cells is restricted by selective processes or is shaped by developmental restrictions on rearrangements remains to be determined. These cells may function in surveillance for signals of trauma by recognizing self products induced by cellular stress.