In order to elucidate the feature of T-cell immune status in umbilical cord blood (CB) from humans, the expression levels of CD3gamma, delta, epsilon, and zeta chain genes in CD4(+) and CD8(+) T cells of CB were analysed by real-time PCR. CD4(+) and CD8(+) T cells sorted from 12 cases of CB and 10 peripheral blood (PB) samples from healthy adults were used in the study. The beta2-microglobulin gene was used as an endogenous reference, and the evaluations of mRNA expression level of each CD3 gene were used by the 2(-DeltaC(t)) x 100% method. In CD4(+) T cells, the expression levels of CD3gamma, delta, and zeta genes (16.54+/-6.49, 3.53+/-1.15, and 5.48+/-1.10%) from CB were significantly higher than those from PB (P=0.001, P=0.017, and P=0.000, respectively). Higher expression levels of CD3delta and zeta genes (3.43+/-1.19 and 5.24+/-1.42%) in CD8(+) T cells from CB were found than those from PB (P=0.000 and P=0.004). Moreover, the expression level of CD3epsilon gene in CD4(+) T cells from CB (13.29+/-5.72%) was significantly different from that in CD8(+) T cells (7.81+/-4.72%, P=0.018). Thus, the expression pattern of four CD3 genes were gamma>epsilon>zeta>delta in both CD4(+) and CD8(+) T cells from CB, while similar expression pattern was found in CD8(+) T cells from PB samples. In contrast, the expression pattern was presented as epsilon>gamma>zeta>delta in CD4(+) T cells from PB. In conclusion, the present study characterized the expression pattern of CD3gamma, delta, epsilon, and zeta chain genes in CD4(+) and CD8(+) T cells from CB, which might be very useful for further understanding the feature of T-cell immune status in umbilical cord blood. Higher expression of CD3 genes in CD4(+) T cells might relate to the strong ability of activation of TCR-mediated signals, and suggests that this is one of the features responsible for the low allo-reactivity of CB T cells.