Eight subjects with acute functional psychoses receiving unmodified electroconvulsive therapy (ECT) at Ibadan were investigated for occult or subclinical internal tissue damage by serial measurements of eight acute phase reactants. Samples of venous blood were collected from each patient at pretreatment, two within treatment, and one at posttreatment. The acute phase proteins assayed were C-reactive protein (CRP), alpha-2-macroglobulin, ceruloplasmin, factor B, C-4 protein, C-3 protein, transferin, and alpha-1-antitrypsin. Except for CRP, the values of the proteins did not change during treatment. CRP values decreased posttreatment and were not detectable in the last sample in five subjects in whom values had been present pretreatment. Our data do not support fears of occult internal tissue damage during unmodified ECT. The consistent decrease in CRP levels posttreatment when patients no longer exhibited psychotic symptoms could not be explained by type of psychosis, intramuscular injections, or changes in drugs and diet; its significance is not known.