The aim of this study was to determine if the qualitative 99Tcm-DTPA captopril radionuclide test (CRT) can help predict the acute detrimental effect of angiotensin-converting enzyme (ACE) inhibitors on renal function in hypertensive patients with solitary kidneys and chronic renal failure. Between 1991 and 1996, eight consecutive patients (6 males, 2 females) aged 27-73 years (mean 49.8 years) with known chronic renal failure and a solitary kidney referred for ACE treatment were included. 99Tcm-DTPA renography was performed at baseline and 1 h after the administration of 25 mg captopril within 1 week of each other. The CRT was performed in accordance with the criteria of the Working Party on the Diagnostic Criteria of Renovascular Hypertension with Captopril Renography. A beneficial or detrimental effect of subsequent ACE inhibitor treatment on renal function was determined by long-term follow-up (> or = 2 years). The CRT accurately predicted outcome in all eight patients subsequently treated with ACE inhibitors. In conclusion, our results suggest a role for qualitative 99Tcm-DTPA CRT in the prediction of renal function in patients with a solitary kidney and chronic renal failure subsequently treated with ACE inhibitors.