Immuno-chemotherapeutic effects on the growth of MM-48 mammary tumor were studied in syngeneic C3H/He mice fed diets containing a low (D), normal (N) or arginine-supplemented (NA) protein content. The serum protein levels were 5.7 g/dl in N-mice and 3.7 g/dl in D-mice, respectively. On the other hand, no difference was seen between the two groups, with regard to intra-tumoral protein concentrations. The natural killer (NK) activity of spleen cells was significantly lower in D-mice than in N-or NA-mice. Augmentation of NK activity was detected following the i.p. injection of OK-432 or LENTINAN, while no augmentation was recognized in D-mice. Interferon production of cultured spleen cells was significantly reduced in D-mice, and significantly increased in NA-mice compared with N-mice. NK activity was markedly augmented at 7 days after bilateral oophorectomy in N-mice. Both NK and IFN titers were significantly reduced following administration of estradiol every 7 days. The growth of MM-48 tumor was inhibited by daily administration of OK-432 or LENTINAN in N-mice. However, the tumor growth was paradoxically accelerated after administration of the same drugs in D-mice. These findings indicated that the nutritional or endocrine environment of cancer-bearing mice plays an important role in the effect of some kinds of BRMs. A clinical randomized study of advanced and recurrent gastric cancer patients treated with MMC and FT (MF) with or without LENTINAN, was then performed. We recognized excellent end-point results only in LENTINAN-administered patients with normal protein levels, while no effect of LENTINAN was seen in patients with low protein levels (below 6.0 g/dl).