The pattern of expression of cytokine mRNA in the lesions of anal furunculosis was evaluated in tissue biopsies from 15 dogs, and compared with the pattern in control skin samples from 24 dogs, by reverse-transcriptase PCR using canine cytokine-specific primers and a semi-quantitative multiplex PCR assay. Interleukin-2 (IL-2) was detected in 11 of the 15 affected dogs but in only one of the controls, and interferon-gamma was detected in 14 of the affected dogs but none of the controls. In contrast, IL-4 was detected only in one of the affected dogs. Increased expression of mRNA for IL-1beta, IL-6, tumour necrosis factor alpha, IL-8, IL-10 and transforming growth factor beta1 was detected in the biopsies from the lesions of anal furunculosis relative to the control tissues (P < 0.05).