Angioscintiphotography with 99mTc has been performed in 310 cases of space-occupying kidney lesions with the purpose of establishing the diagnostic value of the kidney perfusion. In the presence of a neoplasm, a more or less marked blood flow in the lesion generally appears as a hot area. This pattern is not observed in poor vascularized carcinomas or in Wilms' tumors. The percentage of poorly vascularized tumors is moderate and does not affect the value of the method. Cystic lesions appear usually to be cold. Large cysts exhibit no uptake; on the contrary, the degree of vascularization in the small cysts is more difficult to evaluate, as the normally supplied surrounding parenchyma overlaps the cold area caused by the cyst. In the evaluation of the angioscintiphotographic picture, we must take into account the concomitant hepatic or splenic vascularization, which may cause some doubts of interpretation because of projection interferences. The renal angioscintiphotography has an important rule in specifying the nature of a space-occupying kidney lesion and may be regarded as a useful screening test.