BACKGROUND Decreased dopamine beta-hydroxylase (DBH) activity has been reported in unipolar psychotic depression. DBH comparisons between elderly delusional and nondelusional depressives and controls and determination of whether pretreatment group differences persist have not been reported. Our objective was to compare DBH activity in elderly delusional major depressives with that of nondelusional depressives and normal control subjects before and after hospital treatment. METHODS Enzyme activity was assessed after hospital admission. A subsample had predischarge assessments. Treatment was not controlled but accounted for in analyses. Electroconvulsive therapy subjects were medication-free for posttreatment assays. RESULTS Baseline and predischarge DBH assays were lower in subjects with delusional depression than in either comparison group. Despite high intraindividual correlation, treatment was associated with significant increases in activity in the clinical groups. CONCLUSIONS Patients with late-life delusional depression have lower DBH activity before and after hospital treatment than age-matched nondelusional patients or normal controls.