A long-term clinical and therapeutic study was performed in 47 patients with mesangial IgA glomerulonephritis. The male to female ration was 2.9:1. An episode of gross haematuria or the incidental discovery of asymptomatic microscopic haematuria with associated mild proteinuria heralded the apparent onset of renal disease. At the onset of observation 18 patients (38.2%) had high blood pressure. Other 17 patients developed hypertension during observation. Anaemia was uncommon. No essential abnormalities in serum protein and lipid patterns were found. Twenty-nine patients (61.6%) had higher levels of serum immunoglobulins--most frequently of IgA (42.5%). Twenty-two patients had low serum C3 levels (46.8%). The percentage of patients with renal failure increased from 21.2 to 36.1 during observation. Male sex, hypertension, proteinuria higher than 2 g/24 h, elevated ESR, high serum IgA levels, longer duration of the disease and older age of patients suggest an unfavourable outcome. Long-term treatment with a combination of azathioprine/acenocumarol, or indomethacin, or levamisole has no effect on the clinical manifestation and evolution.