[Circadian rhythm of plasm testosterone levels. II. Testosterone levels during the 1st and 2d half-day]

Testosterone in plasma is measured in 50 young males in the morning and in the evening by radioimmunoassay. Peaks are found in the morning. At 07,00 h and 10,00 h the values lie on a plateau: 91,77% at 07.00 h and 90,59% at 10.00 h. The difference is not significant. Significant differences however can be noted in comparison between values in the first and second half-day. The difference between the 07.00 h value and the 16.00 h value amounts to 17,08%; between the 07.00 h value and the 19.00 h value, to 22,6%.