Indications for renal biopsies in isolated hematuria in childhood remain difficult to define. Their limitation to patients presenting with either a macroscopic or a familial hematuria [Trachtman et al. 1984] bears the potential risk of missing the diagnosis of IgA-associated nephropathies (Berger disease and Henoch-Schönlein nephritis) which may manifest themselves by microscopic hematuria only. In order to reevaluate the association between biological IgA abnormalities and mesangial IgA deposits, iterative and concomitant determinations of IgA plasma levels, of IgA immune complexes and of IgA production by lymphocytes in vitro have been performed over a one-year period in two groups of hematuric children presenting with mesangial IgA deposits (14 cases) or not (13 cases). The incidence of positivity of each test was significantly higher in the former group of patients than in the latter. However, the best discrimination between both groups was observed when the three tests were repeated and/or considered together (97% vs 15% of positivity). In Berger disease and Henoch-Schönlein nephritis, IgA immune complexes were the only IgA abnormality more frequently detected in patients presenting with hematuria than in patients presenting with no hematuria at the time of testing. It is proposed to add IgA abnormalities to macroscopic or familial hematuria as indications for renal biopsies in isolated hematuria in childhood.