Tubulointerstitial changes in systemic vasculitic disorders: a quantitative study of 18 biopsy cases. Tubulointerstitial alterations were studied in 18 biopsy cases of systemic vasculitis. To evaluate the changes more objectively, two indexes, the number of interstitial inflammatory cells and tubulitis percentage, were used. The group means of both of these indexes were statistically higher than those of the autopsy control group, while 14 of the cases (77.8%) showed a significant difference (P less than 0.01) between individual means and the control group means. On the other hand, tubulointerstitial changes in systemic vasculitis seemed to be less prominent than drug-induced tubulointerstitial nephritis (TIN) according to these indexes. However, comparing these indexes with those of drug-induced TIN, six cases (33.3%) of systemic angiitis could be regarded as having developed pathologic changes similar to TIN. Statistical difference was not shown in the indexes between those patients with histologic evidence of necrotizing angiitis and those without it. Clinically, urinary N-acetyl-beta-D-glucosaminidase (NAG) was abnormally high in all three examined cases, reflecting the damage of renal tubular epithelial cells. Not only the vascular and glomerular lesions, but also tubulointerstitial changes, should be evaluated in the renal biopsy specimen of systemic vasculitis. 