The effect of bacterial endotoxin (lipopolysaccharide, LPS), on the release of prostaglandin F2 alpha (PGF2 alpha) from human placental explants was investigated. Both LPS and calcium ionophore A23187 stimulated PGF2 alpha release (p < 0.05). Placental explants, either exposed to LPS and A23187 simultaneously or primed by LPS before A23187 stimulation, resulted in similar increased PGF2 alpha releases, which were higher than the level of LPS alone. The data suggest LPS could increase basal PGF2 alpha release from human placenta, combined with A23187 it may act on PG synthase as well in favour of PGF2 alpha formation.