In this study, we examined the effects of 1 and 2 h of brisk walking on post-prandial metabolism. Eleven pre-menopausal women participated in three oral fat tolerance tests with different pre-conditions: control (no exercise), 1 h walk(1 h of walking at 50% maximal oxygen uptake, V O 2max , on the day before) and 2 h walk (2 h walking at 50% V O 2max on the day before). Venous blood samples were taken in the fasted state and for 6 h after ingestion of a high-fat mixed meal. Compared with the control trial, the 1 h walk reduced post-prandial lipaemia by a mean of 9.3%, whereas the 2 h walk reduced it by 22.8% ( P 0.01 for trend). Similarly, the 2 h walk reduced the post-prandial insulin response to a greater extent than the 1 h walk (17.3 vs 7.6%; P 0.05 for trend). The results demonstrate that the beneficial effects of exercise on post-prandial metabolism are related to the duration and, therefore, the energy expenditure of the exercise session.