The responses of plasma testosterone (T), sex hormone-binding globulin (SHBG) binding capacity, androstenedione (A), and luteinizing hormone (LH) to 21 km of marching exercise and to sleep deprivation stress were studied in army recruits. The effect of physical fitness on the exercise responses was evaluated, cross-sectionally, by comparing the stress responses in 11 fit and 11 less fit subjects, and, longitudinally, in 11 subjects after 4 months of physical training. The submaximal marching exercise did not significantly alter the plasma hormone levels compared to the control day levels. The fit subjects had a tendency toward smaller decreases in the mean plasma T and T/SHBG ratio during both control and exercise days than the less fit subjects. After 4 months of conditioning, the mean plasma T and T/SHBG ratio tended to decrease less during both control and exercise days, which was more evident in the well-conditioned subjects. The exercise caused a decrease in mean plasma LH, especially in the less fit subjects. After sleep deprivation stress, the morning levels of plasma T, A, and LH were significantly depressed, as a result of which the normal diurnal variation of the hormones disappeared.