Using analytical data from the literature the tyrosine turnover was calculated by a method published previously by us for 72 potato samples with different rates of browning. The samples included 9 varieties grown at three locations in 1969, which were analysed after harvest and after different times of storage at three temperatures. For 58 samples (81%) this calculation led to the same classification of the varieties as did visual observation of the rate of discolouration. It is concluded that enzymic browning of potatoes is correlated rather with tyrosine turnover, which depends on the concentrations of phenol oxidase, tyrosine, chlorogenic acid, and ascorbic acid, than with any single parameter.