T cell subsets and immunoglobulin (Ig) were observed sequentially with the OKT monoclonal antibodies rosette test and the rate scattering turbidimetry in 13 patients who underwent open heart surgery under cardiopulmonary bypass (CPB) for rheumatic heart diseases (RHD) and congenital heart diseases (CHD), before and after operation. Compared with preoperative values, in the early period after CPB, T helper cells, T helper cells to T suppressor cells ratio and IgG decreased significantly; whereas T suppressor cells increased, in RHD and CHD. The T cell subsets returned to the preoperative levels two weeks after CPB in RHD and CHD. The IgG came back to the preoperative levels two weeks after CPB in RHD and only one week after CPB in CHD.