The metabolic response to a 150 or 400 g 13C-labelled pasta meal was studied for 8 h following rest or exercise at low or moderate workload (n 6). Following rest, the 400 g meal totally suppressed fat oxidation (v. 14.1 g following the 150 g meal) and a small amount of glucose was converted into fat (4.6 g), but fat oxidation remained high in subjects who had exercised following both the small (21.8 and 34.1 g) and large meal (14.1 and 32.3 g). Exogenous glucose oxidation was significantly higher in subjects who had remained at rest both following the small (67.6 g v. 60.4 and 51.3 g in subjects who exercised at low and moderate workloads) and large meal (152.2 v. 123.0 and 127.2 g). Endogenous glucose oxidation was similar in the three groups following the 150 g meal (42.3-58.0 g), but was significantly lower following the 400 g meal in subjects who had exercised at low workload (24.2 v. 72.2 g following rest; and was totally suppressed in those who had exercised at moderate workload. As a consequence, a larger positive glycogen balance was observed in subjects who exercised before the large meal (182.8-205.1 g v. 92.4 g following rest; Total fat oxidation calculated from 08.00 hours to 20.00 hours was similar in subjects who exercised at low and moderate workloads. These results indicate that: (1) de novo lipogenesis, which plays only a minor role for the disposal of an acute dietary carbohydrate load, is totally suppressed following exercise, even when a very large carbohydrate load is ingested; (2) the reduction in glycogen turnover as well as a preferential conversion of glucose into glycogen are responsible for the increase in glycogen stores following exercise; (3) for a similar energy expenditure, exercise at low workload for a longer period does not favour fat oxidation when the post-exercise period is taken into account.