Nuclear magnetic resonance images of the non-dominant cerebral hemisphere were obtained in 20 unipolar depressed patients immediately before and 25 minutes after electroconvulsive therapy (ECT). T1 values rose about 1%. Repeated scanning up to 24 hours after ECT was carried out in 13 of these patients. The greatest change in magnetic resonance images was two hours after ECT, and thereafter images gradually returned to baseline values. There was no correlation between magnetic resonance changes and the time taken to become reorientated after ECT.