We have examined whether Soamsan 1 (SA 1) augment the inhibitory effect of oral administration of Soamsan (SA) on lung metastasis of mouse 816 melanoma cells. The inhibitory effect was slightly enhanced by increase in administration dosage of SA 1. SA 1 as well as SA inhibited effectively the lung metastasis regardless of the pretreatment with anti-mouseNK monoclonal antibody. However, in the case of 2-chloroadenosine-pretreated mice, the inhibitory effects of SA and SA 1 were decreased by 18 and 23%, respectively. In vitro stimulation of the mouse splenocytes with mitogens showed that SA or SA 1 significantly augmented the proliferation of mouse splenocytes. Especially, the activity was more prominent in the presence of a B cell mitogen. LPS than a T cell mitogen, Con A. These results suggest that oral administration of SA 1 or SA inhibited lung metastasis of B16 melanoma cells, possibly through a mechanism mediated by the activation of macrophages and B lymphocytes in the host immune system. However, SA 1 did not showed more significant augment of the activation of immune system than SA.