Introduction: Positive psychotic symptoms are reported to be associated with high dopamine (DA), negative symptoms with low DA activity and serotonin (5-HT) activity may be altered in obsessive-compulsive disorder (OCD). Method: We analysed 24h urine samples in groups of patients with OCD, paranoid and non-paranoid schizophrenia and in healthy controls for supportive evidence. Results: Young unmedicated OCD subjects excreted more adrenaline (AD) and homovanillic acid (HVA) and showed a higher HVA/MHPG metabolite ratio and metabolic rate than healthy controls. Independent of general metabolic rate OCD patients showed higher HVA concentrations which suggests that the relative activity of catecholamine systems in OCD (HVA/MHPG) is due more to high DA than to low noradrenergic (NA) activity. Concentrations of 5-HT were also high in OCD patients. In psychotic patients low levels of DA, HVA, NA and MHPG probably resulted from neuroleptic medication. Conclusions: 1. Patients diagnosed with paranoid psychosis showed higher DA utilization than controls and those with few paranoid symptoms showed high 5-HT utilization. 2. These results support studies suggesting that paranoid psychosis is associated more with increased DA activity (discussed in the context of neuroleptic reactivity), that non-paranoid forms are associated more with increased 5-HT activity and that OCD patients are unusually aroused with high levels of Adrenaline, 5-HT and HVA.