The relative number of peripheral blood T-lymphocyte and its subsets, identified by monoclonal antibodies OKT3, OKT4 and OKT8, and Interleukin-2 (IL-2) were assessed in burn patients by means of indirect immunofluorescence and microassay CTLL-2 3H-TdR incorporation techniques. Comparing with the controls, the relative number of OKT3+ cell in burn patients was decreased occasionally, however, the proportion of OKT4+ cell was significantly reduced and did not recover until the patients were cured. The changes in OKT8+ cell depended on the extent of the burn wound. In minor and moderate burn patients, the proportion of OKT8+ cell was temporarily increased, while in major burn patients, it was increased persistently. The OKT4+/OKT8+ cell ratio declined constantly. The results of the experiment showed that the PBMCs IL-2 production in the patients was persistently lower than normal controls and correlated to the OKT4+/OKT8+ cell ratio. These data indicated that following burn injury, there was insufficiency of relative number in TH cells and relative dominance in Ts cells, which might affect the IL-2 production. These findings suggest that the lowered immunopotency after thermal injury may be attributed to both insufficient TH cells and excessive Ts cells.