The pharmacological function of nacrum secreted by cultured pallium cells of a fresh water oyster was examined. Injections of the cultured mantle tissue solution into mice can reduce the bleeding duration after their tails being cut. The cultured solution and the hydrolysed cultured solution can strengthen the systole of the rat uterus (in vitro) and the toad heart (in vitro), but suppress the systole of rabbit small intestine. This pharmacological function changes with taurine content in the cultured solution. The results indicate that the oyster cells secret nacrum vigorously under cultured conditions in vitro, and the secreted nacrum has the same pharmacological function as the natural pearls.