Concentrations of thiamin were determined in pasteurized and UHT-sterilized milks, yoghurt and kefir samples by high-performance liquid chromatography using a reversed-phase C-18 column connected to fluorescence detector. The linearity, recovery and reproducibility of the method were satisfactory. The thiamin content ranged from 0.305 +/- 0.02 to 0.252 +/- 0.03 mg/l in market milks. Yoghurt samples had higher concentration of thiamin (0.355 +/- 0.04 and 0.404 +/- 0.02 mg/l) than values found in market milks. The least thiamin content was found in kefir (0.175 +/- 0.03 mg/l) among the samples analyzed.