Interleukin-4 (IL-4) plays an important role in several areas of T-cell biology, including the development of Th2 responses and blocking Th1 effector mechanisms mediated by gamma interferon (IFN-γ), such as inducible nitric oxide synthase (iNOS) induction. In this study we investigated the effects of alcohol fractions of the blood shell (blood ark shell), Scapharca broughtonii, on the production of IL-4 from mouse EL4 T cells. Two alcohol fractions (SIII and AII) of the blood shell had stimulatory effect on IL-4 production. The SIII fraction itself significantly induced IL-4 production and IL-4 mRNA expression in a dose dependent manner by EL4 T cells. In contrast, the AII fraction enhanced IL-4 expression in PMA-activated EL4 T cells, whereas the AII fraction itself did not. Furthermore, the stimulatory effect of the alcohol fractions on IL-4 production was closely associated with the increase of NF-AT binding activity, indicating that the alcohol fractions of Scapharca broughtonii stimulated IL-4 production in EL4 T thymoma cells via increased NF-AT DNA binding activity.