Hypocomplementemia is found in all types of membranoproliferative glomerulonephritis (MPGN) but not in all patients. Hypocomplementemia can be ascribed to at least two circulating complement reactive modalities. The activation of the classical pathway produced by circulating immune complexes and the presence in the blood of anticomplement autoantibodies, called "nephritic factor"(NF). The activation of the classical pathway by circulating immune complexes is probably the major mechanism responsible for hypocomplementemia in idiopathic MPGN type I. Nephritic factors have been shown to be responsible for the hypocomplementemia in both MPGN type II and III. NFa is probably the major mechanism responsible for the hypocomplementemia of idiopathic MPGN type II. NFt appears to be solely responsible for the hypocomplementemia in MPGN type III. Judging from the complement profile, NFt also may be present in some patients with MPGN type I. Although infection by meningococcus has been associated with deficiency of any of the plasmatic proteins of complement, it more commonly involves deficiency of the terminal components of the complement pathway(C5-C9). We experienced a patient who had MPGN and meningococcal meningitis. We examined the complement level and significantly lower levels of C3, C5 were found persistently. C7 was low at first and it returned to normal range after 2 months. C9 was normal at first, and was low after 2 months. This is the first reported case in which MPGN with meningococcal meningitis occurred.