A 26-year-old man who had suffered from intermittent chills and fever over a two month period was quite clear of heart or kidney involved developed acute deterioration of renal function. A new pansystolic murmur over the apex of the heart was heard on auscultation, and echocardiography clearly showed a vegetation about 0.7-0.9 cm in size on the atrial site of the mitral value. Laboratory investigation displayed normochromic anemia with negative Coombs' test. Immunological studies were positive for rheumatoid factor and circulating immune complex. High serum levels of erythrocyte sedimentation rate and C-reactive protein, nephritic sediment of urinalysis and negative blood cultures for bacteria, tuberculosis or fungus were also noted. Abdominal sonography showed normal kidney size, bilaterally. Renal biopsy revealed typical crescentic glomerulonephritis. After intravenous penicillin therapy for two weeks, the serum creatinine level recovered from 6.7 mg/dl to 2.0 mg/dl and circulating immune complex disappeared. In consideration of cardiac insufficiency and the potential risk for complications of the vegetation, the patient underwent mitral valve replacement. Four weeks after operation, all the abnormal data had resolved completely. These data suggested that infective endocarditis with rapidly progressive glomerulonephritis is curable by antibiotic therapy and surgical intervention.