Although the use of monoclonal antibodies in the diagnosis of fixed human material is a daily routine, the lack of suitable reagents recognizing epitopes resistant to formaldehyde fixation is an obvious limit to extending this approach to veterinary research and practice. To find reagents that retain their binding capacity to the recognized epitopes in formaldehyde-fixed samples, bovine lymphoid tissue sections were immunostained using various antigen retrieval procedures with monoclonal antibodies raised against ruminant leukocyte cell surface molecules. As a results, a set of antibodies could be established that allowed the identification of different immune cell types including all or a distinct subpopulation of B and T lymphocytes, monocytes, macrophages, granulocytes, red blood cells, and vascular endothelial cells.