The role of viruses in several renal diseases is not documented clearly. The authors attempted to localize envelope glycoproteins of Hantaan virus in biopsy specimens from patients with Korean hemorrhagic fever (KHF) as evidence of direct viral invasion of renal tissues. The authors studied sequential sections of kidney biopsy specimens from 23 of 35 patients with serologically confirmed KHF diagnosed between June 1985 and December 1989. The sections were stained with the avidin-biotin-peroxidase complex method with monoclonal antibodies to G1 and G2 envelope glycoproteins. Control antibodies of the same isotype were used to rule out nonspecific staining, and hyperimmune rabbit sera or convalescent sera of patients with KHF were used for blocking tests. Normal renal tissues and kidney biopsy tissues from minimal-change nephrotic syndrome were used as negative control sections. The kidney biopsies were performed between the fifth and thirtieth days after onset of fever. The authors detected viral glycoproteins in renal tissues from 22 of the 23 patients. The viral glycoproteins were localized in the cytoplasm of the tubular epithelial cells, and the distribution of viral glycoproteins in the tubules was focal. Glycoproteins also were localized in the cytoplasm of the sloughed renal tubular epithelial cells, where tubular degenerative changes were prominent. These findings suggest the direct invasion of renal tubules by the virus and may partly explain the pathogenesis of acute renal failure in KHF.