A patient is described who had accelerated hypertension and unilateral renal artery stenosis, and who developed further deterioration in renal function during treatment with captopril, an angiotension-I (AI) converting-enzyme inhibitor. 99mTc-DMSA uptake was greatly diminished in the stenotic kidney, although renal blood flow and handling of 131I-hippurate was preserved. Uptake of 99mTc-DMSA in the affected kidney returned after substitution of captopril by the vasodilator minoxidil, while a comparable degree of blood pressure control was maintained. Thus, caution must be taken when interpreting results of 99mTc-DMSA scintigraphy in patients with proven or suspected renal artery stenosis treated with an AI converting-enzyme inhibiting drug. Moreover, our finding points to the importance of glomerular filtration in the renal handling of 99mTc-DMSA.