The biologically functional effect of eight kinds of hot-water extracts of shellfish on cultured human cell lines was examined in a serum-free medium model.Meretrix lusoriaandSinonovacula constrictaextracts enhanced IgM secretion of both hybridoma HB4C5 and SI102 cells when cultured with the respective extracts. The purified principle exhibited remarked activity in the adsorbed fraction in hydroxyapatite and Concanavalin A columns. The extracts ofCorbicula fluminea,Crassostreas gigas,Meretrix lusoria,Anadara granosa, andSinonovacula constrictaenhanced in nitroblue tetrazolium (NBT)-reducing ability of macrophage U-M cells.Meretrix lusoria,Anadara granosa, andSinonovacula constrictawere specifically cytotoxic to both cultures of MCF-7 breast cancer cells and HuH-6KK hepatoblastoma. These findings imply that the extracts of shellfish that were examined exhibited a differential effect on immune cells and tumor cells.