Prostaglandin $E_2$(PG$E_2$) is an abundant eicosanoid in bone that has been implicated in a number of pathological states associated with bone loss, and is also known to stimulate matric metalloproteinase-1 systhesis and secretion in rat and human osteoblast cells, although the intracellular reaction remain unclear. Interleukin-1$eta$ (IL-1$eta$) is a cytokine that plays a critical role in bone remodelling and appears to act as a downstream effector of most bone-resorbing agents. However, it is still interesting to examine whether PG$E_2$ regulates IL-1$eta$ expression by mouse osteoblasts or not. Here we demonstrate that PG$E_2$is a potent inducer of IL-1$eta$ production by fetal osteoblasts.