This report describes data collected by the Italian Registry of Renal Biopsies (IRRB) (E mail http://www.teseo.it/nephrology/irrb), which includes 15461 renal biopsies (RB) performed over a period of 7 years (1987-1993). From 1987 to 1988, the Registry recorded only the histological diagnosis of 3686 RB, whereas beginning in 1989, additional records (sex, age, clinical symptoms and renal function) were obtained from 11,775 patients undergoing RB. This is the first report on such a large number of RB containing data from 96% of Italian renal units which routinely perform RB. In 13,835 RB performed in native kidneys, two groups of renal diseases, primary (59.9%) and secondary (25.4%) glomerulonephritis (gn), were more frequent than others. Among primary gn, the frequency of cases of IgAN, membranous gn, and focal and segmental glomerulosclerosis were 36.9, 21.7 and 10.4% respectively. Renal disease due to immune-mediated causes (51%) and dysgammaglobulinaemia (26.9%) were the most frequent among secondary gn. In the former group, the frequency of cases with lupus nephritis and vasculitis were 51.6 and 25.9% respectively. Renal amyloidosis (39.3%), essential mixed cryoglobulinaemia (30.9%), and multiple myeloma were the most frequent forms in the latter group. In 1993 the incidence of the following groups of renal disease was: primary gn (22.7 p.m.p.), secondary gn (11.1 p.m.p.) of which immune-mediated gn (5.8 p.m.p.), dysgammaglobulinaemias associated with nephritis (2.4 p.m.p.). IgAN and membranous gn, as primary gn, had an incidence of 8.4 and 4.9 p.m.p, respectively, while lupus nephritis (2.6 p.m.p.) and renal vasculitis (1.6 p.m.p.) were the most frequent forms of secondary gn. Clinical data regarding 10357 RB collected during 5 years (1989-1993), showed that the most common indications to perform RB were urinary abnormalities (30.8%) and nephrotic syndrome (27.1%), followed by recurrent episodes of macrohaematuria (8.7%) and nephritic syndrome (5.4%). Acute renal failure was present in 9.2% of patients and chronic renal insufficiency in 18.8% of cases. Membranous gn (32.9%), focal and segmental glomerulosclerosis (12.3%), and minimal-change disease (12.0%) were the most frequent diagnoses in patients with nephrotic syndrome, while post-streptococcal gn (16.1%) and IgAN (14.0%) were frequent in the nephritic syndrome. IgAN was frequently found in patients with urinary abnormalities (29.8%) and recurrent episodes of macrohematuria (71.4%). Twenty per cent of the acute renal insufficiency cases were secondary to necrotizing vasculitis, while chronic renal failure was present in 16.6% of the IgAN patients. The IRRB is considering to extend its programme to include (i) paediatric section regarding RB from patients aged less than 18 years; (ii) annual review of clinical data concerning the kidney function of selected groups of patients recorded in IRRB, and (iii) the listing of IRRB records on the INTERNET, to facilitate the distribution of information throughout the scientific community.