A temporal study of the biliary elimination of endogenous 19-nortestosterone during two successive pregnancies was made in three cows with cannulated gall bladders. Bile samples were analysed for 17β-19-nortestosterone (β-NT) and the 17α-epimer (α-NT) by using high resolution gas chromatography and mass spectroscopy. No β-NT was detected in any of the samples analysed. However, α-NT was detected from around 120 days of gestation in each of the cows. Peak concentrations were observed in the last week before calving and ranged from 9.5 to 36.7 ng/ml. After parturition, the concentrations of α-NT declined rapidly and were undetectable by seven days after calving, and it was not detected again until after 120 days of gestation. The biliary concentrations of α-NT detected subsequently were similar to those observed in cattle several weeks after an exogenous injection of the synthetic ester β-NT phenylpropionate.