Previous studies suggest that angiotensin converting enzyme (ACE) inhibitors cause reversible acute renal failure (ARF) in patients with hypertension, congestive heart failure (CHF), and renal disease. These patients often receive diuretics concomitantly with ACE inhibitors. The purpose of this study was to examine whether ACE inhibitors alone produce ARF or whether they do so when used in combination with diuretics. The medical records of patients taking ACE inhibitors without or with diuretics were reviewed. Complete data from 74 patients were obtained and the data were analyzed. These 74 patients had a diagnosis of hypertension, CHF or diabetes mellitus. BUN and serum creatinine values before, during, and after discontinuation of ACE inhibitor therapy for a mean period of 8.7 months were collected. Seventy-four patients were divided into two groups: Group A (n = 41) patients who received ACE inhibitors alone; Group B (n = 33) patients who received a combination of an ACE inhibitor and a diuretic. ARF developed in 1 of 41 (2.4%) Group A patients compared to 11 of 33 (33%) Group B patients. This group difference was highly significant (P < .001). In Group A, mean serum creatinine before (1.24 +/- .34 mg/dl) was identical to that 1.23 +/- .33 mg/dl) after 8.7 months of ACE inhibitor therapy, whereas in Group B, post-mean serum creatinine (3.11 +/- 2.27 mg/dl) was significantly (P < .01) higher than pre-mean serum creatinine (1.65 +/- .85 mg/dl). CHF patients had a higher rate of ARF than patients with other diagnoses. Urinary electrolytes showed that 4 of 6 Group B patients had chloride concentration less than 20 mEq/l.(ABSTRACT TRUNCATED AT 250 WORDS)