The concentrations of testosterone (TS) and other related hormones in serum were examined before and after physical exercise with a bicycle ergometer (90 Watts, 20 min.) and a cold water stimulation in 32 19-year-old males. While exercising, the serum TS level significantly increased by 20.8% (p less than 0.05), the luteinizing hormone (LH) level by 3.6% (p less than 0.05) and noradrenaline (NA) level by 140.0% (p less than 0.01). During cold water stimulation, TS decreased by 10.0%, LH increased by 22.1% and NA decreased by 23.8%. Based on changes in hormone levels within the individual during the loads. there was a significant positive correlation coefficient (r) between TS and LH, and between TS and NA, with r (TS-LH) = 0.399 (p less than 0.05) and r (TS-NA) = 0.481 (p less than 0.05) for physical exercise, while r (TS-LH) = 0.403 (p less than 0.05) and r (TS-NA) = 0.431 (p less than 0.05) for cold water stimulation, respectively. These results suggest that physical exercise increases TS level in serum by increasing LH and NA levels, but these tendencies were not found with cold water stimulation.