The biosynthesis of human immunoglobulin E (IgE) is regulated by a complex network involving T and B lymphocytes. Diseases associated with high serum IgE (sIgE) levels are usually characterized by T cell disorders. Total sIgE level has been found to be of clinical relevance in minimal change nephrotic syndrome. However, the clinical significance has rarely been studied in primary IgA nephropathy (IgA N). We retrospectively studied 99 cases of primary IgA N. There were 59 males and 40 females with a mean age of 30.0 +/- 12.1 years. The mean follow-up duration was 45.9 +/- 31.1 months. Pathological grading was done according to the criteria of Meadow et al. Median sIgE for the entire group was 122.0 IU/ml (range: 2.8-5805 IU/ml) which was significantly higher than the healthy control group (median: 43,7 IU/ml, range: 5.0-1003 IU/ml, p < 0.001). However, when the IgA N cases were stratified into grades, only grade I (median: 514 IU/ml, range: 72.1-5805.0 IU/ml) and grade II (median: 229 IU/ml, range: 5.0-5464 IU/ml) patients had significantly higher sIgE than the control group (p < 0.0005 and p < 0.001 respectively). Patients with nephrotic ranged proteinuria (32 cases) were further classified into "stable" and "progressive" groups. The "stable" group had a significantly higher sIgE level (median: 922.0 IU/ml, range: 2.8-5805 IU/ml), compared to that of the "progressive" group (median: 55.3 IU/ml, range: 5.0-1600 IU/ml, p < 0.02). The effect of aggressive treatment (including corticosteroid and/or cyclophosphamide, cyclosporine) was also assessed.(ABSTRACT TRUNCATED AT 250 WORDS)