Ten endogenously depressed patients were studied before, during, and after electroconvulsive therapy. The nature and severity of depression was measured using the Newcastle Rating and Hamilton Depression Scales. The mean number of treatments administered was 12, and all patients recovered. Regional cerebral blood flow was studied using single photon emission computerized tomography (SPECT) with inhalation of133Xe. The mean values dropped by 8% after session three and a further 13% after the last session. The flow values of untreated patients was significantly higher than those found in 10 healthy volunteers. The values in patients following the last treatment session did not differ from those in the control group. There were no changes in the regional distribution of blood flow between controls and among patients in the three situations studied. No correlation was found between the physiological data and single items from the rating scales used. Increased cerebral blood flow values found in the treatment situation are due to the presence of depressive illness as such and not to agitation or anxiety. The parallel between flow data and clinical data points to the normalization taking place after, and not during, electroconvulsive therapy.