End-stage renal failure requiring dialysis treatment developed within 5 years in 11 patients with IgA mesangial glomerulonephritis (out of 94 affected by this nephropathy) whose serum creatinine levels were less than 2 mg/100 ml at the time of biopsy. We compared these patients (Group 1) with 10 patients (Group 2) whose serum creatinine was comparable at the time of biopsy (1.2 +/- 0.3 vs 1.4 +/- 0.3 mg/100 ml) but remained unchanged (1.1 +/- 0.4 mg/100 ml) at the end of a minimum post-biopsy follow-up of 5 years. The analysis of clinical findings, at the time of biopsy, showed that the mean duration of disease, from apparent onset, was shorter in Group 1. Recurrent macroscopic hematuria, never reported in this group, was present in 40% of patients of Group 2, whereas minimal urinary abnormalities, discovered by chance, were the only findings in 73% of patients of Group 1 and in 30% of Group 2. No difference was present between the patients in the two groups in the amount of proteinuria and in the incidence of high IgA serum levels, whereas hypertension was more frequent (45% vs 20%) in Group 1. The analysis of histological lesions demonstrated that in Group 1 there was a greater incidence of diffuse mesangial proliferation (82% vs 30%), of extensive glomerular obsolescence (64% vs 0) and of severe interstitial fibrosis (54% vs 0). Immunofluorescence findings were similar in the two groups. Although no single clinical or morphological parameter was characteristic of the patients with subsequent rapid decline of renal function, some features were more commonly observed, or more severe, in these patients, and therefore should be considered reliable predictors of an unfavourable outcome.