The studies presented in this report were designed to evaluate whether bacterial endotoxin alters the rate of biosynthesis of prostaglandin E2 (PGE2) by human amnion. Amnion cells were established in primary monolayer culture from women undergoing elective cesarean sections. Endotoxin from Escherichia coli and Salmonella typhosa were incubated with amnion cells for 16 hours, and radioimmunoassay was used to measure PGE2 released into the media. Bacterial endotoxin demonstrated a concentration-dependent stimulatory effect on the rate of PGE2 synthesis by amnion cells. These observations suggest a mechanism for the onset of labor associated with intra-amniotic infection.