Abstract. The purpose of this study was to compare the immunoreactivity in canine renal tissues stained with antisera specific for 3 leptospiral antigens and those processed with traditional staining methods. In addition, immunoglobulin staining was done on tissues with immunoreactivity to leptospiral antigens. Formalinfixed renal sections from 12 dogs with chronic interstitial nephritis suspected or proven to have leptospirosis (6 dogs with silver-stained leptospires and 6 dogs in which silver-stained leptospires were not detected) were used. Antibodies consisted of a monoclonal antibody to Leptospira kirschneri serovar grippotyphosa lipopolysaccharide (LPS) and 2 polyclonal antibodies to outer membrane proteins, including OmpL1, a leptospiral porin, and LipL41, an outer membrane lipoprotein. The murine monoclonal antisera against LPS (F71C2-1) had the most abundant and consistent immunoreactivity. Immunoreactive areas were present in 6 of 6 sections positive by silver staining and included extracellular granular debris in intertubular areas, debris in macrophages, organisms in tubular lumina, and cytoplasmic granules in tubular epithelia. Antisera with specificity for the outer membrane proteins OmpL1 and LipL41 detected only intact organisms in tubular lumina. Immunoreactivity to OmpL1 (polyclonal 338) occurred in 4 of 5 sections positive by silver staining, but immunoreactivity to LipL41 (polyclonal 813) occurred in only 1 of 6 silver-positive sections. Each of the kidney sections in which leptospiral antigens were detected by immunohistochemistry also was positive by silver staining. Sections negative by silver staining were also negative by immunostaining. Although immunohistochemistry did not enhance sensitivity, amplification of signal by secondary antibody and hematoxylin counterstaining improved the ease of diagnosis and allowed better evaluation of tissue morphology than did silver staining methods. IgG was the most abundant immunoglobulin. IgG immunoreactivity occurred predominantly in plasma cells within interstitial infiltrates. Interstitial infiltrates contained abundant immunoreactivity to LPS, but immunoreactivity to OmpL1 and LipL41 was not noted.