In diabetic patients disturbances of pituitary-gonadal axis are observed. The aim of the study was to investigate whether in male diabetic patients the circadian rhythms of FSH, LH and testosterone are maintained normal and whether the treatment in a health resort affects the circadian rhythms of investigated hormones. The study regards 5 male patients with insulin dependent diabetes mellitus type I and in 10 male patients with diabetes mellitus type II. In order to assess the circadian rhythm serum FSH, LH and testosterone were determined four times a day at 6.00, 12.00, 18.00 and 24.00. Serum concentration of FSH and LH was determined by LIA and testosterone by RIA. The investigation was done twice: on the third day of a health resort treatment and then on the 23rd day of the treatment. The results were analysed using the Cosinor test. It has been shown that the circadian rhythm of LH, FSH and testosterone is maintained in diabetic patients. During the health resort treatment the midline value (mesor) of serum concentration and the amplitude of of circadian rhythms of LH and testosterone increased in diabetic patients, whereas the FSH circadian rhythm did not change. During the health resort treatment a significant change of testosterone circadian rhythm acrophase from 7.32 to 5.16 was observed in diabetic patients.