Recent studies have shown an increased gastrointestinal reactivity and increased intestinal permeability in IgA nephropathy (IgAN). Probiotic supplementation is known to impact the gastrointestinal immune system possibly by improvement of both the immunologic and the non-immunologic intestinal barrier. Probiotic supplementation should thus theoretically have an effect on IgAN. In this study the investigators will study the efficacy and safety of Lactobacillus reuteri.

Inclusion Criteria:

• Above 18 years
• Primary IgAN, verified by biopsy
• Albuminuria > 0.75 g/24 h (verified by at least four sample results within a two years period prior to inclusion)
• Serum creatinine less than 200 umol/L (verified by at least four sample results within a two years period prior to inclusion)
• Having signed informed consent form

Exclusion Criteria:

• Participation in another clinical intervention trial
• Patients with celiac disease
• Patients with secondary IgAN
• Creatinine clearance below 30 ml/min (mean of 3 measurements)
• Introduction of an ACE inhibitor or angiotensin II receptor blocker during the last three months prior to inclusion
• Patients treated with immunosuppressive or systemic corticosteroid drugs within the last twelve months
• Patients using probiotic products within the last three months (includes probiotic milk products)
• Known allergy or intolerance to any of the ingredients in the probiotic product