MHPG excretion of 14 endogenously depressive patients and 5 healthy controls was investigated before, during and after a night of sleep deprivation (SD). Patients having a minimum improvement of 40 % in the Cronholm-Ottoson rating scale had shown a significantly higher MHPG excretion in the night before SD (p < 0.02) as compared to the non-improved group. The MHPG excretion of the night before SD shows a significant negative correlation, both with the depression score according to Cronholm-Ottoson (p < 0.05) and with the self-rating score according to von Zerssen (p < 0.005), on the day after SD. No correlation was found between the motor activity measured by pedometer and MHPG excretion. The results are discussed in connection with values found in controls.