1. Serum bile acids in seven patients with adult type myotonic dystrophy and 22 normal persons were quantitatively analysed by gas—liquid chromatography and gas chromatography—mass spectrometry for cholesterol, γ-glutamyltransferase and bilirubin. There was no bile obstruction in any patient.
2. Deoxycholic acid values in all mothers of patients with congenital type myotonic dystrophy were three times (2.1 μmol/l) that of the control (0.7 μmol/l).
3. Uncommon bile acids were detected in the patients' sera. One of them appeared to be dihydroxymono-oxocholanic acid, having a longer side chain. Another one appeared to be dihydroxycholanic acid, with a steroid-nucleus structure similar to chenodeoxycholic acid and with a longer side chain.
4. Biliary bile acids from three patients and one normal person were also analysed, and this revealed a remarkable decrease in ursodeoxycholic acid in the patients.
5. The presence of bile acid abnormality in patients with myotonic muscular dystrophy is proposed.