Federal law prohibits pre-employment physical examination of firefighter recruits, but these workers must perform intense exercise in arduous environments. Components of physical fitness of rookie firefighters (n ϭ 115; 104 men, mean Ϯ SD: age ϭ 28.3 Ϯ 4.3 years; height ϭ 1.76 Ϯ 0.07 m; weight ϭ 83.2 Ϯ 13.9 kg; percent body fat ϭ 17 Ϯ 8%) were measured upon being hired and following a 16-week exercise training program (1 h·d Ϫ1 , 3 d·wk Ϫ1 ) designed to improve physical fitness. Maximum aerobic capacity (V O 2 max) was estimated from submaximal cycle ergometry, body composition from skinfold tests, flexibility from a sit and reach test, strength by hand grip dynamometry, and muscle endurance by a push-up test. The results are as follows (*, p Յ 0.007 vs. pretraining): V O 2 max increased by 28% (35 Ϯ 7 to 45 Ϯ 6* ml·kg Ϫ1 ·min Ϫ1 , 88 Ϯ 20 to 113 Ϯ 17%* of predicted increase); muscle endurance increased (41 Ϯ 13 to 51 Ϯ 14* push-ups); flexibility increased (0.34 Ϯ 0.07 to 0.35 Ϯ 0.07* m); muscle strength tended to increase (102.9 Ϯ 18.7 to 105.4 Ϯ 18.7 kg, p ϭ 0.06); body weight tended to decrease (83.2 Ϯ 13.9 to 82.7 Ϯ 13.2 kg, p ϭ 0.06); lean tissue weight increased (68.8 Ϯ 9.9 to 69.9 Ϯ 9.5* kg); and fat weight decreased (14.6 Ϯ 8.0 to 13.0 Ϯ 7.1* kg). We concluded that aerobic capacity was 20% lower before training than that deemed sufficient for safe performance of fire suppression duties; that training improved aerobic capacity by 28%, decreased fat and increased lean tissue weight, and increased/ tended to increase other components of physical fitness. Prior to initiation of this training program, aerobic capacity of these firefighters was below that deemed appropriate for performing fire suppression duties. Training resulted in a large increase in aerobic capacity, so that the trainees ended the program with an aerobic capacity considered appropriate for fighting fires. It is hoped that the results of this study will encourage those who oversee workers who are responsible for the public's safety to mandate assessment of physical fitness of new hires, with mandatory participation in exercise training for those new hires who are found to possess less than appropriate aerobic capacity.