The expression of the mRNAs of the cytokines interleukin (IL)-1 alpha, IL-1 beta, IL-2, IL-4, IL-6, interferon (IFN)gamma, tumour necrosis factor (TNF)alpha, and granulocyte-macrophage colony-stimulating factor (GM-CSF) was demonstrated by the reverse transcription-polymerase chain reaction (RT-PCR) in bovine alveolar macrophages (AMs) and peripheral blood mononuclear cells (PBMCs). By the use of the RT-PCR, a specific and highly sensitive technique has been developed to analyse simultaneously the array of cytokine messenger RNAs in bovine AMs and PBMCs. AMs stimulated with lipopolysaccaride (LPS) for four hours in vitro expressed IL-1 alpha, IL-1 beta, IL-6, TNF alpha and GM-CSF; PBMCs stimulated with LPS for four hours expressed IL-1 alpha, IL-1 beta, IL-6, TNF alpha and GM-CSF and when stimulated with concanavalin A (ConA) expressed IL-2, IL-4, IFN gamma and GM-CSF efficiently.