Since IgA nephropathy can be experimentally induced by alimentary antigens, mechanisms of oral immunization might be supposed also in human primary IgA nephropathy (PIgAGN). IgA immune complexes (IgAIC) are thought to play a major role in PIgAGN, hence this parameter was monitored in six PIgAGN patients subjected to diets excluding gluten, meat or eggs respectively and selected as having persistent urinary activity and high IgAIC levels. On gluten-free diet IgAIC significantly decreased over 3 different periods of 10 days (Student's t-test p 1 less than 0.03, Rank-Signed test p 2 less than 0.02), 1 month (p 1 less than 0.007, p 2 less than 0.02) and 6 months (p 1 less than 0.05, p 2 less than 0.02). IgAIC significantly increased again on a gluten containing diet over 1 month (p 1 less than 0.008, p 2 less than 0.04) and 3 months (p 1 less than 0.02, p 2 less than 0.04). After 6 months on a gluten-free diet, all patients had normal IgAIC values and decreased IgA2 subclass-IgAIC, in agreement with the hypothesis of withdrawal of an antigen challenging the mucosal immune system. These data indicate a relationship between a gluten-containing diet and high levels of IgAIC in PIgAGN patients, suggesting that dietetic factors might play a role in the different geographical distribution of this nephropathy.