The concentrations of 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxyindole-3-acetic acid (5-HIAA) and homovanillic acid (HVA) were determined in CSF of patients with hypoxia due to circulatory arrest. Patients were divided into neurologically disabled and recovered according to the Glasgow Coma Scale. CSF was collected 4, 28, 76 and 172 h after commencement of resuscitation and once from control patients subjected to spinal anaesthesia. The initial concentrations of MHPG, 5-HIAA and HVA were significantly higher in a subgroup of neurologically disabled patients who died within 76 h. In recovered patients the concentration of MHPG declined with time to the value of the control group, whereas it increased in neurologically disabled patients. In the latter group the concentration of 5-HIAA also showed an increase with time, whereas in recovered patients it declined after an initial rise. It is concluded that high concentrations of MHPG, 5-HIAA and HVA in CSF may be prognostic for hypoxic brain injury after cardiac arrest.