The immunological effect of an extract from Momordica cochinchinensis seed (ECMS) on immune responses against infectious bursal disease (IBD) in chickens was evaluated. Fifty-two birds were equally divided into 4 groups and immunized with inactivated IBD vaccine alone (controls) or IBD vaccine emulsified with ECMS (20, 40, and 80 microg). Serum IgG antibody levels against IBD and BW were measured on 0, 7, 14, 21, 28, and 35 d after immunization. The ELISA results revealed that the chickens that received 20 microg of ECMS had significantly enhanced antibody levels on 14, 21, 28, and 35 d when compared with controls (P<0.05). A significant increase in mitogenic stimulated lymphocyte proliferation was also recorded in all ECMS groups as compared with controls (P<0.05; P<0.01). No adverse effect of ECMS was noted on growth performance, although average weight gain was significantly higher in 20 microg (7, 14, 21, 28, and 35 d) and 40 or 80 microg (14 d) of ECMS groups as compared with controls (P<0.05; P<0.01). Further studies are suggested for the investigation of immunological effects of ECMS.