Abstract Prostaglandin production in amnion and decidua is considered important for human parturition. We investigated in pregnant guinea pigs, a species similar to women in regard to the endocrinology of pregnancy, whether the production rates of PGE 2 and PGF 2α in various intrauterine tissues are compatible with a role in parturition. Net production rates were measured at 45, 55 and 65 days of gestation and during labor in amnion, chorion, myo-endometrium, the outer layer of the myometrium, the site of placental implantation, and placenta. Net production rates in amnion increased between 45 days and labor (30-fold for PGE 2 and 8-fold for PGF 2α, P < 0.0001). During labor, the production rates in amnion of PGE 2 (P = 0.006) and PGF 2α (P = 0.019) were higher than at 45, 55, and 65 days of gestation. In myo-endometrium, the production rates of PGF 2α were higher at 65 days of gestation than at 55 days and during labor (P = 0.046). Addition of arachidonic acid (10 −5 M) increased production of PGE 2 and/or PGF 2α in all tissues (P < 0.05) except placenta. In amnion, the response to arachidonic acid increased with advancing gestation. This suggests that 1) PGE 2 and PGF 2α produced by amnion have a potential role in the initiation and maintenance of labor, 2) PGF 2α produced by myo-endometrium has a potential role in the initiation of labor, 3) cyclooxygenase(s) are not rate-limiting except in placenta, and 4) the expression of cycloxygenase in amnion increases with advancing gestation.