Semiquantitative reverse transcription-polymerase chain reaction was used to analyse the expression of cytokine mRNAs in freshly isolated peripheral blood mononuclear cells obtained from a patient with Kimura's disease. The patient was treated with cyclosporin A (CsA) after incomplete tumour resection and irradiation of lesions. Levels of interleukin (IL)-4, IL-5 and IL-13 mRNA were elevated and the level of interferon (IFN)-gamma mRNA was within normal limits before treatment. The levels of IL-4, IL-5 and IL-13 mRNA, the number of eosinophils, and the serum level of IgE decreased markedly after surgery and radiation therapy. CsA treatment suppressed these values in a dose-dependent manner, but had a minimal effect on the level of IFN-gamma mRNA. The number of peripheral eosinophils decreased in association with decreases in the levels of IL-4, IL-5 and IL-13 mRNAs during CsA therapy; the serum level of IgE remained low during therapy and did not fluctuate in association with changes in cytokine levels. These results suggest the Th2 cytokines play a part in the development of Kimura's disease and that CsA suppresses the activity of this disease.