Diurnal Testosterone Levels in Peripheral Plasma of Human Male Subjects

A diurnal variation of testosterone in the peripheral plasma of adult male subjects has been observed. Significantly greater quantities of the hormone (p<0.01) were found at time 0800 when compared to the levels in the afternoon or in the evening. Also, the plasma concentration of testosterone was higher on 2 consecutive mornings compared to the intervening evening. The magnitude of this diurnal variation was not so great as that reported for plasma Porter-Silber chromogens or for conjugated dehydroepiandrosterone.