Mesangial IgA nephropathy was experimentally induced in ddY mice by oral and parenteral administration of the poliomyelitis vaccine (POLIO), and we then tried to investigate if IgA deposition could be prevented by the concurrent use of sodium cromoglycate (SCG), which is known to inhibit the local mucosal immune reaction. Mucosal and systemic immunity could be induced by the administration of POLIO; proteinuria, increased serum IgA levels, mesangial cell proliferation, mesangial matrix widening, mesangial deposits of IgA, and large electron dense deposits in the mesangium were observed. Concurrent administration of SCG and POLIO resulted in a significant decrease in the serum IgA level and mesangial IgA deposits. The later addition or abstinence of SCG after the 70th day did not influence the glomerular mesangial IgA deposition. But the serum IgA level was still decreased by the continuous treatment of SCG even after the 70th day. Thus, mesangial IgA nephropathy simulating IgA nephropathy in humans could be induced in ddY mice using POLIO and its induction could largely be prevented by the concurrent use of SCG. However mesangial IgA deposits already present could not be cleared by the late administration of SCG.