Acetazolamide, furosemide, chlorothiazide, and amiloride are pharmacologic agents that act primarily in the proximal tubule, loop of Henle, early distal tubule and late distal tubule and collecting duct, respectively. In order to investigate the renal pathophysiology induced by amphotericin B, these diuretic agents were used as probes of discrete segments of the nephron in the neonatal rat. Six-day-old rats were treated with amphotericin B (20 mg/kg, sc) or the vehicle. Twenty-four hours later, when evidence of amphotericin B-induced renal pathophysiology is detectable, the responses to the diuretic agents were assessed in a 2-hr clearance test, during which creatinine clearance (CCr) and the fractional excretion (FE) of water and various components of the filtrate were determined. Amphotericin B induced alterations in basal function including azotemia, hypostenuria, increases FE water and electrolytes, and a decreased FE urea (although CCr was normal). All of the diuretic agents elicited an increase in urea excretion in amphotericin B-treated pups such that FE urea approached control values. (Copyright (c) 1988 Academic Press, Inc.)