The mesangioproliferative glomerulonephritis (MPGN) is the most frequent morphological type of primary glomerulonephritis and it was found in 42.7% of the patients studied. The MPGN is not a single nosologic entity which is proved by the immunofluorescent findings, clinical and laboratory characteristics. Several immunofluorescent types with characteristic clinico-laboratory constellation and different etiopathogenesis could be defined. The most clearly defined types of MPGN are those with leading IgA and IgM precipitates. The similar immunofluorescent findings, clinico-laboratory characteristics, course and susceptibility to symptomatic and pathogenetic treatment in MPGN with leading IgG and C3 precipitates lead to the suggestion that there may exist different "phase" states in the course of the different types of MPGN. In spite of some characteristic differences in the symptomatology and course of the different types of MPGN their differentiation is possible only by kidney biopsy.