The aim of our study was to assess the prevalence of the specific disorders of the circadian rhythm of cortisol and melatonin in the patients with sleep disorders. The group of our patients consisted of 93 persons (25 men, 68 women), from 4-72 years (mean age 38.3 years) with a sleep disorders. These patients were studied on Department of Neurology of 1st Medical Faculty of Charles University in Prague during years 1997-1999. Patients were divided by the clinical diagnosis into many subgroups: idiopathic hypersomnia (IH) 24 patients and other hypersomnias 8, narcolepsy 22, degenerative disorders 9, delay sleep phase syndrome (DSPS) 7, periodic leg movements syndrome (PLMS) 6, insomnia 7 and Parkinson's disease 10 patients. Twelve salivary samples were taken from each patient during a period of 24 hours in order to investigate the circadian secretion pattern of melatonin and cortisol. Salivary melatonin and cortisol levels were estimated by radioimmunoassay in the Department of Physiology of the Academy of Science, Czech Republic. Significant differences were found between our patients and the control group in idiopathic hypersomnia--acrophase of melatonin was delayed and secretion was prolonged. Patients suffered from narcolepsy often displayed multiple peak of melatonin secretion. The peak of the melatonin concentration occurred later in DSPS (non significantly). Low level of melatonin and prolonged signal of melatonin was in Parkinson's disease patients.