Phosphoethanolamine and taurine have been identified in uterine extracts from rat and, for the first time, human tissue. The concentration of phosphoethanolamine [PEtn] determined by HPLC and 31P NMR spectroscopy, increased markedly (40%) within the first 6-12 h following parturition in rats, suggesting a role in involution. It appears that changes in [PEtn] account for the changes in the NMR phosphomonoester peak previously reported. A significant fall in [PEtn] was found in the human myometrium with pregnancy. Taurine was found in high concentrations in the rat and human uterus but decreased with pregnancy. The possible functional significance of these changes is discussed.