Urinary secretory IgA (slgA), consisting of free secretory component (FSC) and dimeric IgA, is involved in the defense against urinary tract infections (UTI). Recurrent UTIs (rUTI) have been suggested to be associated with a defective excretion of slgA. Therefore urinary slgA, FSC and serum-type IgA concentrations were measured by ELISA in 68 normal women, 10 asymptomatic women with rUTIs and no urological abnormality (group A), 8 asymptomatic women with rUTIs and a urological abnormality (B), 4 women with acute UTI (C) and 5 women with a selective serum IgA deficiency (D). Annual UTI rates were increased in groups A, B and C, but normal in group D. In no patient group urinary FSC concentration was different from the normals, while slgA concentrations were increased in group C, markedly reduced in group D, but normal in groups A and B. Urinary serum-type IgA concentrations were significantly increased in group A and C, markedly reduced in group D and normal in group B. These results demonstrate that the urinary s IgA system participates in the immune response to bacterial infections, but that even a complete failure of the slgA system does not lead to an increased UTI rate. Furthermore, no association of recurrent UTIs with disturbances of the urinary slgA excretion could be demonstrated.