Glucose pre-treatment enhances ageing in excised roots of tomato on subsequent sub-culture in sucrose medium to a much greater extent than pre-treatment in sucrose or fructose. However, continual sub-culture in glucose medium causes much less ageing than continual sub-culture in sucrose or fructose. Sugar concentrations used were such as to preclude effects due to osmotic potential changes. Pre-treatment in mixtures of glucose and sucrose caused less ageing than glucose alone, but this may be due to the demonstrated reduction in glucose absorption caused by sucrose. A two-stage system for the development of ageing is proposed and this is discussed in the light of earlier studies on ageing in cultured tomato roots.