N-Nitroso-N-methyldodecylamine and N-nitroso-N-methyltetradecylamine, which cause urinary bladder tumours in experimental animals, were detected in several hair-care products formulated with N,N-dimethyldodecylamine oxide. Quantitative determinations were made using a gas-liquid chromatograph interfaced with a thermal energy analyser and using [1-14C]N-nitroso-N-methyldodecylamine as an internal standard. The presence of the two nitrosamines was confirmed by high-pressure liquid chromatography with a thermal energy analyser as detector, by photolysis of samples and by combined gas chromatography-mass spectrometry. To test the reproducibility of the method, a single shampoo was selected for replicate analysis and was found to contain 90 ± 8 ppb N-nitroso-N-methyldodecylamine and 37 ± 11 ppb N-nitroso-N-methyltetradecylamine. Levels of N-nitroso-N-methyldodecylamine in other hair-care products ranged from 11 to 873 ppb and those of N-nitroso-N-methyltetradecylamine from 8 to 254 ppb.