Several zinc parameters were assessed in 13 patients with essential hypertension who were chronically taking only captopril (six subjects) or enalapril (seven subjects), as well as in six untreated hypertensives, and nine healthy controls. Serum zinc levels were comparable in all groups. Twenty-four-hour urinary zinc excretion was significantly increased in the captopril-treated patients compared with the other three groups. The zinc:creatinine ratio in 24-hour urine was significantly increased in both captopril and enalapril groups, but was significantly greater in the former. Although plasma zinc concentrations were comparable in all groups, red blood cell (RBC) zinc values were significantly decreased in the captopril group compared with the other three groups. We conclude that (1) although both captopril and enalapril produce renal zinc loss, this loss is far greater in patients receiving captopril; and (2) captopril administration over 3 months or more generates RBC zinc depletion.