Isolated viable hepatocytes of human fetuses (weeks 12-34 of gestation) were prepared by collagenase/hyaluronidase digestion of liver slices. These cells have the ability to catalyze certain metabolic transformations involved in the disposition of xenobiotics. The levels of enzymes catalyzing oxidative metabolism (phase I) were very low in the fetal liver cells, although such cells possess appreciable metabolic capacity to catalyze synthetic (phase II) reactions. These cells retained the ability to metabolize 7-ethoxycoumarin when maintained in short term, nonproliferating monolayer culture for up to 4 days. The metabolism of 7-ethoxycoumarin was significantly increased by treatment of cells with 1,2-benzanthracene, but not with phenobarbital. The usefulness of isolated fetal human hepatocytes both in suspension and short term culture as model systems for the study of developmental aspects of the enzymes involved in the metabolism of foreign compounds and as a tool for study of various toxic effects of chemicals on the human fetus is discussed.