Diuretic radionuclide urography is a modification of conventional renography which utilizes the administration of intravenous furosemide to distinguish dilated, non-obstructed, hydronephrotic systems from those with significant mechanical obstruction. Diagnostic patterns are derived from computer generated time-activity histograms that depict the accumulation and washout of radiotracer before and after diuretic injection. In dilated but non-obstructed systems, diuresis produces a decline in activity. In obstructed systems, there is a failure of radiotracer washout in response to diuresis and no decline in activity is observed. The procedure is applicable to patients of all ages with suspected upper urinary tract obstruction. Clinical and experimental data support the accuracy and utility of this methodology and define its limitations and pitfalls.