Formalin-fixed, paraffin embedded tissues obtained from 40 pigs inoculated with a field isolate of hog cholera virus were examined for the presence of Gp55, a major structural protein of the virus envelope, using a monoclonal antibody-based immunohistochemical test with the avidin-biotin-peroxidase complex method. Immunoreactivity was detected in hog cholera virus-infected tissues but not in control pigs tissues, African swine fever virus-infected tissues, or bovine viral diarrhea virus-infected porcine or bovine tissues. The first positive reactions were seen in lymphatic tissues, digestive tract and skin on postinoculation day (pid) 4, respiratory and urinary tissues on pid 5, nervous tissues on pid 6, and endocrine tissues on pid 7. These staining reactions persisted until the last observation on pid 18. Hog cholera virus antigen was not detected in heart tissue at any time. The highest levels of antigen detection were found in tonsils, spleen, and pancreas, although the esophageal mucosa and skin epithelial cells were also intensely and widely stained. The cellular staining pattern of Gp55 had a ubiquitous distribution. It was found in epithelial cells, macrophages and circulating monocytes, endothelial cells, lymphoid cells, and glial cells. The results showed a high specificity and high sensitivity for detecting hog cholera Gp55 in formalin-fixed, paraffin embedded tissue samples. This method allows precise association of Gp55 with specific cells, tissues, and histologic lesions, making the technique suitable for use in routine diagnosis of hog cholera.