A severely ill 65-year-old man presented with symptoms of shortness of breath, edema and vasculitidic purpura over his lower extremities. He had severe mitral regurgitation which had not been surgically treated. Hematologic examination demonstrated leukocytosis with profound anemia. Other blood tests revealed impaired renal function, hypoalbuminemia, hypocomplementemia and mixed-type cryoglobulinemia. Urinalysis showed proteinuria, hematuria and pyuria, typical of a nephritic sediment. Renal biopsy indicated diffuse proliferative glomerulonephritis and a "full house" deposition in immunofluorescence study (positive for C3, C4, C1q, IgG, IgA and IgM), resembling the pathologic findings in class IV lupus nephritis. Although subacute bacterial endocarditis was initially suspected owing to a history of a predisposing valvular heart disease, probable vegetation shown by cardiac sonography and a clinical picture suggestive of a chronic infection, it was thought unlikely due to the entire afebrile course and initial sterile blood cultures. However, the blood cultures repeated 2 weeks after admission grew 3 sets of viridans streptococci. Following a course of penicillin and gentamicin treatment, his renal function, anemia and abnormal urine sediments improved gradually. Diffuse proliferative glomerulonephritis is well known to occur in infective endocarditis. However, the "full house" immunostaining in immunofluorescence study has never been reported. This case adds a new entity to the differential diagnosis of "full house" immune complex-related glomerulonephritis and exemplifies the need to maintain a high index of suspicion for underlying infectious disorders when facing glomerulonephritic or vasculitic syndrome.