Semiquantitative reverse transcription-PCR assays were developed to measure feline interleukin-2 (IL-2), IL-4, IL-5, IL-6, IL-10, and IL-12 (p35 & p40); gamma interferon (IFN-); and glyceraldehyde-3-phosphate dehydrogenase mRNA concentrations in biopsies of feline oral mucosa. Biopsies were collected from 30 cats with chronic gingivostomatitis (diseased) prior to each cat receiving one of four treatments. In 23 cases replicate biopsies were collected 3 months after treatment commenced. Biopsies were also analyzed from 11 cats without clinical disease (nondiseased). Expression of IL-2, IL-10, IL-12 (p35 and p40), and IFN- was detected in most nondiseased biopsies, while IL-6 was detected in a minority, and IL-4 and IL-5 were both undetectable. Compared to nondiseased cats, the diseased population showed a significant increase in the relative mRNA expression of IL-2, IL-4, IL-6, IL-10, IL-12 (p35 and p40), and IFN-. In contrast, IL-5 mRNA expression was unchanged and was only detected in one case. No significant relationship was demonstrable between the change in relative expression of specific cytokine mRNA and the change in clinical severity of the local mucosal lesions over the treatment period. The results demonstrate that the normal feline oral mucosa is biased towards a predominantly (Th) type 1 profile of cytokine expression and that during the development of lesions seen in feline chronic gingivostomatitis there is a shift in the cytokine profile from a type 1 to a mixed type 1 and type 2 response.