Plasma neurotransmitters and cortisol in duodenal ulcer patients. Role of stress. Levels of noradrenaline, adrenaline, dopamine, free serotonin, platelet serotonin, and cortisol were measured in the plasma of duodenal ulcer patients and controls. All subjects received antacids, and these substances were also measured. During relapse, all patients showed raised noradrenaline, adrenaline, dopamine, free serotonin, and cortisol values. In contrast, platelet serotonin showed very low values, which correlated negatively with all the former, except free serotonin. No correlations were found in parameters of the controls. After healing, significant reductions of noradrenaline, adrenaline, dopamine, free serotonin, and cortisol and significant increases of platelet serotonin values were observed. However, only dopamine, free serotonin, and cortisol reached normal values. Noradrenaline and adrenaline remained higher and platelet serotonin lower, both significantly more so than normals. These still-altered parameters showed similar correlations to those found during relapses. The present results demonstrate that some baseline autonomic system imbalance exists in patients, amplified and accentuated during relapse. We discuss the possibility that stress plays some role in triggering duodenal ulcer relapse. 