A case of SLE with moderately deteriorated renal function due to lupus nephritis developed cryptococcal meningitis. Long term administration of amphotericin B (cumulative dose 5 g) combined with 5-flucytosine eradicated this fungal infection. Throughout amphotericin B administration urinary excretions of Na and K, as well as plasma HCO3 concentration were monitored, and, Na, K and HCO3 were supplemented orally and intravenously so much as to replace their urinary losses. Neither prominent water-electrolyte disturbance nor severe azotemia, which are the most serious side effects of amphotericin B, did not ensue. This case study indicates that sufficient water.electrolytes supplementation is important to prevent the nephrotoxicity of amphotericin B.