31 samples of potato varieties with slow, medium and fast rates of browning were studies. Characteristic enzyme patterns were obtained from polyacrylamide gel electrophoresic of the phenoloxidases of varieties with different discolouration rates. The differences lie mainly in the intensities of the enzyme bands. The qualitative determinaiton of the phenols showed no significant differences. Tyrosine, chlorogenic acid and caffeic acid produce coloured oxidation products; the characteristic colour gradations of in vivo browning were only observed in the presence of tyrosine. It is concluded that the same reactions take place during the discolouration of all the varieties.