OBJECTIVE Urinary secretory IgA (sIgA), an immunoglobulin synthesized locally in mucosal surface is an important immunological defense in preventing bacterial adherence to periurethral epithelia and uroepithelia. Therefore attempts were made to measure secretory IgA in the urine of children with urinary tract infections (UTI), by using sIgA specific ELISA. METHODS Fresh or unprocessed urine samples from healthy donors (children and adults N=10 each), 68 children and 17 Adults with UTI were tested for the presence of sIgA. RESULTS The level of sIgA in 10 healthy normal children was 2.7 +/- 0.94 ug/ml and that in 10 healthy adults was 5.2 +/- 0.73 ug/ml. Children with UTI showed highly elevated levels of sIgA amounting to 279 +/- 80 ug/ml (p<0.001). It was interesting to note that 96% of children and 76% of adults with UTI had sIgA level significantly above that of +/- 2SD of respective controls (287 +/- 99 and 80 +/- 48 ug/ml respectively). On culturing the urine obtained from these children the colonies identified were E. coil about 46%, Klebsiella about 24% and Pseudomonas about 24%. The sIgA antibody from urine samples assessed by indirect immunoflourescense. specifically reacted with the respective organism. CONCLUSIONS Taken together the results show that the presence of sIgA not only correlated with the UTI in children as well in adults but sIgA seems to be directed to the infective agent and can also be used to identify the type of infection. Thus measurement of urine antibody levels may provide an alternative marker of host responses to infection, which can be used either as a simple screening test or could be useful to assist alongwith other tests in establishing a diagnosis.