OBJECTIVE To investigate the expression of alpha-smooth muscle action (alpha-SMA) in the renal tubulointerstitium in patients with kidney collateral stasis. METHODS The expression of alpha-SMA in the renal biopsy specimens from 54 patients with kidney collateral stasis was examined by immunohistochemical method. RESULTS The degree of kidney collateral stasis was increased with the increasing of the degree of renal interstitial fibrosis (P