Of 17 renal units from 11 patients treated with intrarenal bacillus Calmette-Guerin (BCG) for positive selective upper tract urine cytology 16 had negative radiographic studies and 1 had a papillary renal pelvic lesion. The standard diagnostic maneuvers were used to rule out other sources of positive cytology from the lower tracts. Six patients had bilateral involvement, 3 had prior contralateral nephroureterectomy and 2 had unilateral positive cytology but were poor surgical risks. The BCG solution was administered weekly by retrograde ureteral catheterization and instillation during 1 hour. One patient had fever during the initial treatment and received antituberculous therapy. Other side effects included transient hematuria in 3 patients and irritative urinary symptoms in most patients. Of 11 patients (12 renal units) 8 had normalization of the urinary cytology with a median followup of 36 months. One patient had unilateral conversion of the cytology result but the contralateral papillary tumor persisted, requiring nephroureterectomy. The remaining 2 patients had persistently positive cytology results and the disease progressed. Longer followup and further experience with intrarenal BCG are required before the exact role of this treatment modality in upper tract urothelial malignancies, including carcinoma in situ, can be determined.