The cytokine mRNA profiles of the bovine mammary gland were investigated using newly developed TaqMan real-time polymerase chain reaction systems (Applied Biosystems, Foster City, CA, USA). Transcriptional activity of six cytokines, interleukin (IL)-2, IL-6, IL-12, interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and granulocyte-macrophage colony stimulating factor (GM-CSF) was studied during the mid- and late-lactation stages. Transcripts for TNF-alpha, GM-CSF, and IFN-gamma were detected in all samples of both stages. However, IL-12 was only detected in 80 and 58 % of late- and mid-lactation samples, respectively. IL-12 expression was up-regulated in late lactation in comparison with the corresponding level in mid-lactation. The cytokines interaction in late lactation was more co-ordinated and their transcriptional levels were significantly correlated among each other, whereas, in mid-lactation significant correlation of the cytokines transcription was only seen with the TNF-alpha, GM-CSF, and IFN-gamma. Cytokine mRNA profiles between mid- and late lactation showed significant differences, which can be attributed to the dramatic changes that the mammary gland is subjected to during late lactation. The significant elevation of IL-12 transcriptional activity in late lactation and its relevance to the mammary gland immunity is discussed.