The aim of this study was to determine the relative abundance of prostaglandin G/H synthase-1 (PGHS-1) mRNA in human amnion, choriodecidua and placenta obtained before (n = 5), during (n = 5) and after spontaneous-onset labour and delivery at term (n = 5). PGHS-1 mRNA relative abundance was not affected by labour status (p > 0.1) nor differently expressed between gestational tissues (p > 0.05). These data are consistent with the hypothesis that PGHS-1 is a constitutively expressed isozyme and that an increase in the relative abundance of mRNA encoding this enzyme is not necessary for the labour-associated increase in prostaglandin formation.