The generation and output of PGE2 and PGE1 by isolated rat uterus incubated with or without glucose as well as the influence of different metabolic substrates and selective enzyme inhibitors on tissue formation and release of PGE material of the 1 and 2 series, were explored. The output of PGE2 was comparable with glucose, fructose, lactate or pyruvate as the substrate but diminished significantly in citrate-containing solution. In substrate-free media uteri released more PGE2 than in the presence of glucose or other substrates. The PGE1 liberated was similar in glucose, fructose, lactate or pyruvate and decreased significantly in citrate or without substrate. 2-deoxy-D-glucose (2-DG), fluoride or arsenite failed to alter significantly the release of PGE2 whereas 2,4-dinitrophenol (DNP) evoked augmentation. The uterus released less PGE1 after 2-DG or fluoride but not following the addition of DNP or arsenite. The results suggest that the synthesis and release of PGE2 and PGE1 in the isolated rat uterus appear to be selectively modulated by different tissue metabolic pathways.