Fifteen depressed patients were treated with increasing doses of bromocriptine in an open study. Twelve were treated for 5 weeks (final dose 20-60 mg daily) and nine of these recovered almost completely. As expected from a dopamine agonist, bromocriptine decreased the level of homovanillic acid (HVA) in cerebrospinal fluid (CSF) by 15% (P less than 0.05) and 23% (P less than 0.01) after 2 and 5 weeks of treatment, respectively. After 2 but not after 5 weeks of treatment there was also a small but significant decrease (13%; P less than 0.001) of the noradrenaline metabolite HMPG in CSF. Although there was no mean effect on 5-HIAA in CSF, there was a significant relationship between the HVA and 5-HIAA levels (as % of pretreatment level) both after 2 and 5 weeks of treatment (r = 0.96 and r = 0.62, respectively). This may indicate that the drug has an effect on the serotonin system secondary to the dopamine receptor stimulation. The amelioration of depression was not related to HVA, but did correlate to HMPG in CSF (r = 0.65; P less than 0.05) both metabolites measured before treatment. These results indicate that bromocriptine may have antidepressant effects possibly mediated through the noradrenergic system rather than the dopaminergic system.