Gamibojungikki-tang (GBIT) has been used for the purpose of development of physical strength in Korea. We investigated the anti-immobility effect of GBIT on the forced swimming test (FST) and then measured the blood biochemical parameters related to fatigue, glucose (Glc); blood urea nitrogen (BUN); lactic dehydrogenase (LDH); creatine kinase (CK) and total protein (TP). GBIT (0.01, 0.1, 1 g/kg) was orally administered to mice for 7 days. After 7 days, the immobility time was significantly decreased in the GBIT-administration group (105.0+/-12.1 s for 1 g/kg) in comparison with the control group (152.3+/-16.2 s). The contents of Glc and TP in the blood serum were significantly increased in GBIT-administration group (1g/kg) compared with control group, while LDH was significantly decreased. Surface phenotyping of spleen cells by FACS analysis revealed an increasing tendency of CD4+ and CD8+ number, without statistical significance. In addition, GBIT (0.01-1 mg/ml) increased the interferon-gamma and interlukin-2 levels in MOLT-4 T-cells. These results suggest that GBIT may be useful in the immune function improvement.