Riboflavin, a water-soluble, light-sensitive vitamin, was determined in dairy products from Turkish supermarkets. High-performance liquid chromatography was used with a reversed-phase C18 column and ultraviolet-visible detection. A solvent system of water-methanol (70:30 v/v) with acetic acid (1,5 ml) in water (1 l) and a flow rate of 0.5 ml min(-1) gave the most appropriate separation of riboflavin at 270 nm. The linearity, recovery and reproducibility of the method were satisfactory. The riboflavin content ranged from 1.391 to 1.159 mg l(-1) in pasteurized milks, from 1.532 to 1.302 mg l(-1) in UHT milks, from 1.662 to 1.302 mg kg(-1) in yoghurts, and from 3.681 to 1.479 mg kg(-1) in pickled White cheeses. When the opened containers of UHT milks were stored in a refrigerator at 5 degrees C, in the dark, the loss of riboflavin ranged from 1.84 to 6.05% of the initial values.