The effect of frying conditions on the colour changes during deep fat frying of french fries has been investigated. The Hunter colour scale parameters redness, yellowness and lightness were used to estimate colour changes during frying as a function of the main process variables (oil temperature, oil type and sample thickness). A first-order kinetic equation was used for each one of the three colour parameters, in which the rate constant is a function of the main process variables. The results showed that oil temperature and thickness of potato strips have a significant effect on the colour parameters, which are not affected by the use of hydrogenated oil in the frying medium. (C) 2001 Elsevier Science Ltd. All rights reserved.