Inbred strains of rats and mice have long been used to study basic mechanisms of human disease. Our knowledge of the rodent and human immune systems has increased in recent years, largely because of the availability of reagents and techniques specific for these species. In contrast, outbred animals, including domestic companion and food animals, have not been used routinely as experimental models for human disease, largely because reagents and assays necessary for basic research in immunology and physiology have not been available. Here, using consensus cytokine nucleic acid sequences, we adapt a previously described reverse transcription-quantitative competitive polymerase chain reaction technique to measure interleukin 2 (IL2), IL4, IL6, IL10, IL12, interferon, gamma tumor necrosis factor alpha, and glyceraldehyde-3-phosphate dehydrogenase mRNA expression in the cow, cat, dog, horse, and pig. We demonstrate that the assay is sensitive, accurate, and reproducible.