Endogenous concentrations of prostaglandin (PG) F-2 alpha in the rabbit uterus were higher on Day 17 of pseudopregnancy than on Days 4, 7 and 11 of pseudopregnancy and Day 17 of pregnancy. These differences are consistent with the findings reported previously that the output of PGF-2 alpha from the rabbit uterus is higher on Day 17 of pseudopregnancy than on earlier days of pseudopregnancy and Day 17 of pregnancy. Uterine homogenates synthesized PGs and, of the 3 PGs measured, 6-oxo-PGF-1 alpha was the major product. There were no differences in the amounts of any one PG synthesized during pseudopregnancy. 'unstretched' uterine tissue from Day-17-pregnant rabbits produced quantities of PGs similar to those of uterine tissue from Day-17-pseudopregnant rabbits. However, 'stretched' uterine tissue from Day-17-pregnant rabbits produced more 6-oxo-PGF-1 alpha and PGE-2, but not PGF-2 alpha, than did 'unstretched' tissue or pseudopregnant uterine tissue from Day-17 rabbits. PG production by the fetal placenta was higher than that by the maternal placenta. PGE-2 and 6-oxo-PGF-1 alpha were the major PGs produced by the fetal and maternal placentae, respectively. Metabolism of PGF-2 alpha required NAD+ and metabolism by the placenta was greater than that by the uterus. Compounds less polar and more polar than PGF-2 alpha were produced, although the production of more polar metabolites appeared to require a period of progesterone priming of the uterus.