OBJECTIVE To detect anti-tubular basement membrane antibodies in sera from patients with tubulointerstitial nephritis (TIN) and investigate its clinical significance. METHODS The sera were studied from 46 patients with renal biopsy proven TIN. The normal human renal cortex was obtained from patients with nephroectomy, far from carcinoma. Tubules were isolated by a differential sieving technique. The fragments of renal epithelia were removed from tubular basement membrane enriched materials by sonication and centrifugation. Tubular basement membrane antigens were solubilized with 6 mol/L guanidine-HCl. The soluble proteins were used as antigens in Western blot analysis to detect autoantibodies in sera from patients with TIN. The clinical characteristics of positive and negative patients were statistically analyzed. RESULTS Eleven patients with tubulointerstitial nephritis had anti-tubular basement membrane antibodies by Western blot analysis, and seven protein bands could be blotted by the TIN sera. The positive prevalence of anti-55x10(3) antibody (63.8%) was higher than that of other antibodies. Eight of 27 (29.6%) patients with acute tubulointerstitial nephritis and four of 19 (21.1%) patients with chronic tubulointerstitial nephritis had anti-tubular basement membrane antibodies. ESR,serum IgG and IgM in patients with acute TIN with positive anti-tubular basement membrane antibodies were higher than those of the negative group. There was no significant difference in the other clinical variables such as gender,age,hemoglobin,complement C3,serum IgA,serum creatinine,blood urea nitrogen and creatinine clearance in patients with acute TIN between the positive and negative groups. There was no significant difference in clinical variables mentioned above in patients with chronic TIN between the positive and negative groups. CONCLUSIONS Circulating anti tubular basement membrane antibodies could be detected in sera from some patients with TIN, and autoimmunity may play a role in the pathogenesis of TIN.