The aim of this study was to determine the expression of three proinflammatory cytokines by pulmonary macrophages of sheep in paraffin wax-embedded tissue. Samples of lung from seven healthy sheep were fixed by immersion in either 10% neutral buffered formalin, acetic formalin, paraformaldehyde-lysine-periodate or Bouin's solution and processed for structural and immunohistochemical studies. The expression of interleukin (IL)-1alpha, IL-6 and tumour necrosis factor (TNF)-alpha by pulmonary intravascular macrophages (PIMs) and alveolar macrophages (AMs) was detected by the avidin-biotin-peroxidase (ABC) technique. Bouin's solution proved to be the most suitable fixative and Tween 20 the most effective pretreatment for increasing permeability. Constitutive expression of IL-1alpha, IL-6 and TNF-alpha by both macrophage populations was detected. The number of PIMs expressing IL-1alpha (the predominant cytokine in ovine lung) was higher than that of AMs, while the expression of IL-6 was greater in AMs. No differences between PIMS and AMs were found in respect of TNF-alpha expression. The evaluation of cytokine expression represents a valuable tool for studying the pathogenesis of disease in the ovine lung.