The rearrangement segments of TCR Valpha40 gene with Jdelta1, Ddelta3 or psi Jalpha were amplified in genomic DNA from peripheral blood mononuclear cells of 10 normal subjects, sorted CD3(+) cells from peripheral blood of 4 cases and thymocytes from 7 cases, by using nested PCR. Different amounts of DNA from all samples were amplified to estimate the frequency of Valpha40 gene rearrangements. The results indicated that the rearrangements of TCR Valpha40 gene with Jdelta1, Ddelta3 or psi Jalpha could be found respectively in the most samples of peripheral blood T cells or thymocytes. The frequencies of Valpha40 rearrangements were different in peripheral blood T cells and thymocytes by analysis of PCR with different amounts DNA. It is concluded that the TCR V alpha40-psi Jalpha was the most frequent rearrangement in mature and immature T cells, whereas TCR Valpha40-Ddelta3 was more frequently rearranged in immature T cells