To study the effects of a protein bound polysaccharide (PSK) on the immune system in normal animal, lymphocytes subsets of both peripheral (PBL) and thoracic duct lymphocytes (TDL) were analyzed in 6 week old male SPF Wistar-Imamichi rats before and after free feeding of forage which contained 2% of PSK. PBL and TDL were obtained at the time before, 4 weeks after and 8 weeks after administration of PSK. Age matched rats without administration of PSK were used as a control. Following the peripheral blood cell counts were carried out, lymphocytes subsets such as ratio of total T cells helper/inducer T (Th) cell, suppressor/cytotoxic T (Ts) cell and B cell were assayed using W3/13, W3/25, 0 X 8 and 0 X 4 monoclonal antibodies with laser flow cytometric technique (Orthospectrum III Orthodiagnostics). In terms of the PBL, number of total T cells and Th cells in PSK treated group were significantly lower than that of controls. However no statistical different could be obtained between these two groups in relation to the number of Ts cells and B cells. On the other hand, the number of T cells and Th cells in TDL of PSK treated groups were significantly higher than that of controls while Ts cell and B cell number did not show no apparent differences between these two groups. These findings indicate that oral administration of PSK have a potency to accelerate the transport of T cells from blood stream to lymphatic channel and also regulate their distribution in a normal healthy animals.