Muller et al. analysed gamma-glutamyl transpeptidase (GGTP) activity in the amniotic fluid of more than 2000 pregnant women for a prenatal diagnosis. They reported that at 18-19 weeks' gestation, two fetuses associated with lower amniotic fluid GGTP levels were diagnosed after birth as having biliary atresia (BA). If low GGTP values correlate closely with BA, chemical assay of amniotic fluid GGTP could possibly be used in the prenatal diagnosis of BA. A fetal model of cholestasis in the rat was created by the administration of the toxic cytopharmacological agent phalloidin on day 15 of gestation, after which amniotic fluid was aspirated and analysed for GGTP. Fetal liver specimens were examined histopathologically. In the normal rats, amniotic fluid GGTP values rose rapidly after 18 days 8 h, reaching a maximum value at 19 days of gestation. Significantly lower GGTP values were observed in the cholestasis models between 18 days 16 h and 19 days 16 h of gestation (P < 0.05). Our data corroborate Muller et al.'s suggestion that fetuses with cholestasis might demonstrate lower GGTP values in their amniotic fluid at a given stage of gestation. Prenatal diagnosis of BA using the amniotic fluid GGTP assay therefore has considerable potential.