Glutathione S-transferase, glutathione peroxidase, glutathione reductase and gamma-glutamylcysteine synthetase activities were measured in fetal rat liver and placenta supernatant at the 16th and 20th days of pregnancy. Compared with adult liver, low activities were found in both fetal liver and placenta. Both selenium-dependent and selenium-independent glutathione peroxidase activities were present in fetal liver, but only the selenium-dependent activity augmented as parturition advanced. Selenium-independent glutathione peroxidase was found to be absent in placenta. The progress of gestation is accompanied by a significant increase in conjugating capacity toward 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene and a significant decrease toward 1,2-epoxy-3-(p-nitrophenoxy)propane in fetal liver. Glutathione S-transferase activity in rat placenta diminished from day 15 to day 20 of gestation. The elevation of enzymatic activities involved in the synthesis and recovery of glutathione, which takes place in fetal liver and placenta, was thought to be adaptively responsive to the changes that occurred in glutathione-consuming enzymes.