The clinical course and the changes of the levels of immunological factors after tonsillectomy in several cases of IgA nephropathy associated with chronic tonsillitis are presented in this paper. In the first study, here called Part I, 16 cases of IgA nephropathy were observed with regard to the clinical course and the changes of immunological factors after the operation. Postoperatively, proteinuria disappeared in 9 cases and improved in 3 and the levels of serum IgA, the circulating immune complex (CIC) and serum polymeric IgA decreased. In the next study, Part II, 10 cases of IgA nephropathy were investigated regarding the changes of the levels of serum IgA, C3, C4, CH50, APCH50 and CIC after the provocation test and tonsillectomy. A tendency of decreasing levels of C3 and APCH50 combined with an increase of CIC was observed within one week after provocation. Decreases in the levels of serum IgA, polymeric IgA, C3 and APCH50 were also observed after the operation. From these results, it is suggested that the tonsillar lesion has a tendency to continue the pathogenetic effect on the disease and exacerbate its clinical symptoms.