Renal haemodynamics and urinary protein excretion (UPE) were investigated in 36 patients with IgA nephropathy more than 3 years after renal biopsy (mean interval 6.3 +/- 0.5 years). At follow-up, 39% of patients had a reduced glomerular filtration rate (GFR) and 11% endstage renal failure. Twenty-five percent had albuminuria, and a further 25% microalbuminuria. All albuminuric patients had GFRs below the mean, and 78% of the albuminurics had a reduced GFR. However, non-albuminurics also had decreased GFRs and GFR tended to fall with the duration of the disease in this group of patients. On comparing the histological changes in the biopsies with haemodynamic and UPE studies performed 6 years later, we found significant correlations between the extent of segmental glomerular sclerosis and GFR, effective renal plasma flow, urinary albumin and IgG excretion, respectively. Histological grading correlated with the same variables. Of the 4 uraemic patients, 2 were nephrotic at presentation, while the other 2 had a nephritic onset of disease and later developed heavy proteinuria. Three of their biopsies showed > or = 10% segmental glomerulosclerosis. Juvenile IgA nephropathy is not a harmless disease. Our results indicate that these children should be carefully monitored with adequate GFR measurements and urine protein analyses.