The circadian rhythm of melatonin secretion was studied by measuring the amount of its decomposition product (6-sulfatoxymelatonin) in discrete urine sample collected during daytime and night-time periods. The study included a total of 29 subjects ten of whom suffered nocturnal sleep deprivation. 6-sulfatoxymelatonin in the patients of the latter group was measured twice throughout the study: during the 24-hour period with normal sleep and during the 24-hour period with nocturnal sleep deprivation. It was shown that nocturnal sleep deprivation resulted in the disturbances of the circadian rhythms of melatonin production. It sharply decreased at night-time to the levels characteristic of daytime secretion. In the subjects with the normal sleep regimen (i.e. without nocturnal deprivation) the daytime adiponectin levels amounted to 63-75% of the average daily value.