Tissues from nine ferrets with granulomatous lesions similar to those seen in feline infectious peritonitis were examined histopathologically and immunohistochemically. Four main types of lesions were observed: diffuse granulomatous inflammation on serosal surfaces; granulomas with areas of necrosis; granulomas without necrosis; and granulomas with neutrophils. Other less commonly seen lesions were granulomatous necrotizing vasculitis and endogenous lipid pneumonia. FCV3-70 monoclonal antibody produced immunolabelling of group 1 coronavirus antigen in tissue samples from eight animals, the antigen being present in the cytoplasm of macrophages in the different types of granulomatous lesions.