The subjects of this double-blind, randomized, crossover study were 50 healthy male sports teachers aged 21 to 47 years. Every day for six weeks each subject received two capsules of a preparation containing ginseng extract, dimethylaminoethanol bitartrate, vitamins, minerals, and trace elements, or two capsules of placebo. The subjects then performed an exercise test on a treadmill at increasing work loads. The total work load and maximal oxygen consumption during exercise were significantly greater after the ginseng preparation than after placebo. At the same work load, oxygen consumption, plasma lactate levels, ventilation, carbon dioxide production, and heart rate during exercise were significantly lower after the ginseng preparation than after placebo. The effects of ginseng were more pronounced in the subjects with maximal oxygen consumption below 60 ml/kg/min during exercise than in the subjects with levels of 60 ml/kg/min or above. The results indicate that the ginseng preparation increased the subjects' work capacity by improving muscular oxygen utilization.