Two patients, one with ulcerative colitis, the other with Crohn's disease, developed glomerulonephritis due to IgA mesangial deposits. Following symptomatic treatment of the intestinal disease, haematuria subsided in both patients while a second renal biopsy showed disappearance of the mesangial proliferation and IgA deposits. It is suggested that the intestinal and the renal diseases may be linked by abnormal secretion of IgA by the intestinal mucosa with formation of immune complexes, subsequently trapped in the glomerular mesangium.