Disagreement concerning serum angiotensin-converting enzyme (ACE) levels in patients with chronic renal failure has been observed in recent reports. Because ACE is considered as a useful tool for the diagnosis and management of sarcoidosis, and because chronic renal failure may be associated with sarcoidosis, the present work was designed to reinvestigate the possible changes of serum angiotensin-converting enzyme activity in a series of 36 non-hemodialysed consecutive patients with chronic non-sarcoid renal failure. Enzyme activity was significantly lower (p less than 0.004) in the patients (15.8 +/- 5.0 units/ml, mean value +/- 1 SD) than in 47 healthy controls (20.2 +/- 7.6 units/ml, mean value +/- 1 SD). Serum angiotensin-converting enzyme and creatinine clearance values were significantly correlated in these patients (p less than 0.0002). These results indicate that, in non-hemodialysed patients with chronic renal failure, serum angiotensin-converting enzyme levels may not be useful in establishing the diagnosis of sarcoidosis.