The purpose of this study was to examine the effect of an 18-wk weight-training program on average daily metabolic rate (ADMR). Before the intervention and in weeks 8 and 18 (T0, T8, and T18, respectively) data on body composition, sleeping metabolic rate (SMR), food intake, energy cost of the weight-training program (EEex), and nontraining physical activity (accelerometer) were collected in the exercise group (EXER, n = 18 males). ADMR was determined in a subgroup (EX12, n = 12) by using doubly labeled water. At T0 and T18, data (except ADMR) were also collected in a control group (Con, n = 8). Body mass did not change in EXER or Con. Fat-free mass increased only in EXER with 2.1 +/- 1.2 kg, whereas fat mass decreased in EXER as well as Con (2.0 +/- 1.8 and 1.4 +/- 1.0 kg, respectively). Initial ADMR (12.4 +/- 1.2 MJ/day) increased at T8 (13.5 +/- 1.3 MJ/day, P < 0.001) with no further increase at T18 (13.5 +/- 1.9 MJ/day). SMR did not change in EXER (4.8 +/- 0.5, 4.9 +/- 0.5, 4.8 +/- 0.5 kJ/min) or Con (4.7 +/- 0.4, 4.8 +/- 0.4 kJ/min). Energy intake did not change in EXER (10.1 +/- 1.8, 9.7 +/- 1.8, 9.2 +/- 1.9 MJ/day) or Con (10.2 +/- 2.6, 9.4 +/- 1.8, 10.1 +/- 1.5 MJ/day) and was systematically underreported in EX12 (-21 +/- 14, -28 +/- 18, -34 +/- 14%, P < 0.001). EEex (0.47 +/- 0.20, 0.50 +/- 0.18 MJ/day) could only explain 40% of the increase in ADMR. Nontraining physical activity did not change in both groups. In conclusion, although of modest energy cost, weight-training induces a significant increase in ADMR.