PURPOSE: This study examined adaptations in body composition and physical fitness during a 21-wk strength and/or endurance training period in 40- to 65-yr-old men. We also compared the usefulness of different methods for the analysis of body composition to detect training-induced adaptations. METHODS: Fifty-three men were randomized into the endurance training (E: N = 14), strength training (S: N = 13), combined strength and endurance training (SE: N = 15), or control (C: N = 11) groups. S and E trained 2 and SE 2 x 2 times a week for strength and endurance. RESULTS: Percentage of fat (fat%) decreased (5-8%) similarly in all training groups. Fat% measured by DXA at baseline and its change correlated with those recorded by bioimpedance (r = 0.90 and 0.66), skinfolds (r = 0.80 and 0.78), and waistline (r = 0.84 and 0.74). Lean mass in legs (DXA) increased only in S (2.0 +/- 1.5%, P < 0.001), but the thickness of vastus lateralis and intermedius measured by ultrasound increased (7-11%) in all training groups, and that of triceps brachii increased in S (22%) and SE (20%). Maximal concentric force increased significantly in S, SE, and E (by 22, 23, and 7%), and maximal oxygen uptake increased in both E (11%) and SE (11%). CONCLUSIONS: Waist circumference and skinfold thickness seem to reasonably assess changes in percent body fat during training. However, only DXA was capable to separate small differences between the groups in training-induced changes in lean body mass. Combined strength and endurance training is of greater value than either alone in optimizing body composition or improving physical fitness in older men.