Nocturnal patterns of growth hormone (GH) in obsessive compulsive disorder (OCD), which is physiologically released predominantly during the first half of night, have not been reported. However, altered GH responses to pharmacological challenges suggest a disturbed function of the somatotropic axis in OCD. In this study, nine inpatients with a DSM-IV diagnosis of OCD without comorbid major depression (Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score >15; HAMD-21 total score 16) and 9 healthy matched controls were included. Blood of patients (7 males, 31.8+/-9.3 years, Y-BOCS: 27.3+/-4.3, HAMD-21: 13.3+/-1.9) and controls (7 males, 31.6+/-9.1 years) was drawn every 20 min between 2300 and 0700 h during sleep using a long catheter for later GH analysis. Mean plasma GH levels peaked at 0040 h, however this peak was significantly blunted in patients (maximum 4.3+/-1.5 ng/ml) compared to controls (maximum 12.3+/-4.0 ng/ml; p<0.05). In patients but not controls two other, smaller peaks were observed (0220 and 0620 h). In patients but not in controls, GH values exceeding maximum GH values of the peak at 0040 h were observed already at 2300 h or during the second half of night. In conclusion, our results indicate that the nocturnal GH secretion in patients with OCD is altered compared to controls.