Salsolinol and salsoline were labelled with deuterium using an acidic exchange reaction in 2HCl--2H2O. Two deuterium atoms were incorporated in both compounds. The deuterium-labelled salsolinol and salsoline were used as internal standards to determine picomol amounts of the corresponding unlabelled compound in the urine, cerebrospinal fluid, brain and liver. The salsolinol was purified on alumina and salsoline collected in the effluent. The compounds were analysed as their pentafluoropropionyl derivatives by gas chromatography on a 1% OV-17 column and were selectively detected with electron-impact mass spectrometry at the molecular ions M+ and M+--15. With human urine the precision of the methods were +/- 4.9% (coefficient of variation, n = 10) for salsolinol and +/- 2.2% for salsoline at a level of 0.100 nmol/ml. Administration of salsolinol to rats intraperitoneally (0.4 mmol/kg) resulted in levels of 1--2 nmol/g in striatum and limbic forebrain after 2 h, whereas the corresponding liver values were about 550 nmol/g. Control animals showed salsolinol values in liver of about 2 nmol/g and in striatum and limbic forebrain 1 nmol/g tissue.