The conditions surrounding tinea pedis infection were surveyed--the degrees of infection and of aggravation attendant upon training, and the skin temperature within the leather boots of members of the Japanese Self-Defense Forces undergoing winter and summer ranger training. Before winter training, tinea pedis was diagnosed in 8 of the 15 subjects. The mean atmospheric temperature was 7.1 degrees C, the total precipitation, 23 mm, and the mean skin temperature of the feet during training, 33.7 degrees C. After training, 1 further subject had contracted tinea pedis, 5 of the 8 showed slight aggravation, and 3 showed no change. Before summer training, tinea pedis was found in 9 of another 15 subjects. The mean atmospheric temperature was 20.0 degrees C, total rainfall, 353 mm, and the mean skin temperature of the feet during training, 36.6 degrees C. After the training, aggravation had occurred in 3 of the 9, and slight aggravation in the other 6. In these 9, vesiculation, pustules and erosion were seen, so that summer training had a more severe effect than winter training. Investigation of the predisposing factors for tinea pedis due to the wearing of boots and shoes is considered extremely important for the prevention and treatment of this disease.