Hot water polysaccharide extracts of Anacyclus pyrethrum (L.) Link. (family Compositae) Citrullus colocynthis (L.) Schrad. (family Cucurbitaceae) and Alpinia galanga (L.) Willd. (family Zingiberaceae) were tested for their immunostimulating activity in mice. The fractions from Anacyclus pyrethrum and Alpinia galanga showed a marked stimulating effect on the reticulo-endothelial system (RES) and increased the number of peritoneal exudate cells (PEC), and spleen cells of mice. In this case, the optimum doses were 50 and 25 mg/kg for the two fractions, respectively. On the other hand, the polysaccharide extracts of both Anacyclus pyrethrum and Alpinia galanga markedly enhanced the proliferation of the murine spleen cells in vitro using two tests (in vitro and in vivo effect). The results of the in vivo effect at a doses of 50 and 25 mg/kg, showed a stimulation index better than obtained with the in vitro effect at 50 and 25 microg/ml for Anacyclus pyrethrum and Alpinia galanga, respectively. While the extract of Citrullus colocynthis showed much weaker and variable immunostimulating activity.