This study examined the effects of oral administration of an enzymatic protein hydrolysate from green microalga Chlorella vulgaris (Cv-PH) on the recovery of both innate and specific immune responses of undernourished Balb/c mice after a 3-day fasting period. Cv-PH was prepared by hydrolysis of ethanol-extracted cell biomass with pancreatin (20 AU/g) at pH 7.5 and 45 degrees C for 4 h. The treatment with Cv-PH (500 mg/ka) for 8 days provided benefits in terms of haemopoiesis, as judged by the recovery of bone marrow cellularity and the leukocyte counts in peripheral blood, particularly the lymphocyte pool, which increased up to 128% compared to control animals. Starved mice treated with Cv-PH showed a higher number of peritoneal exudate cells and the macrophage activation was demonstrated by the enhancement in glucose consumption and acid phosphatase activities relative to non-supplemented mice. The increased carbon clearance in peripheral blood suggested the stimulation of mononuclear phagocytic system. Cv-PH also stimulated both humoral and cell mediated immune functions positively, such as T-dependent antibody response and the reconstitution of delayed-type hypersensitivity response (DTH). These findings indicate that Chlorella protein hydrolysate can be used for developing physiologically functional foods with immunopotentiating activity. (c) 2006 Elsevier Inc. All rights reserved.