Allergic rhinitis is an IgE mediated atopic disease characterized by elevated levels of allergen specific IgE antibodies that play a central role in mediating allergic reactions. Interleukin 13 (IL-13) is a novel T-cell-derived cytokine that shares several functional properties with IL-4 and has been demonstrated to be capable of inducing IgE synthesis. The present study was designed to investigate the expression of IL-13 gene in the epithelial compartment of the nasal mucosa of patients with perennial allergic rhinitis (PAR) to house dust mite, comparing it with that in the nasal epithelial compartment of chronic infectious rhinitis (CIR) patients and normal volunteers (NV). We also investigated the IL-13 gene expression in the peripheral blood of PAR patients. Nasal scrapings were collected from the inferior turbinate of patients undergoing conchotomy surgery and from outpatients, and the mRNA expression of IL-13 was analyzed by the RT-PCR method. Peripheral blood mononuclear cells were isolated by density-gradient centrifugation and the expression of IL-13 gene was examined by the RT-PCR method. IL-13 expression at protein level and its cell source were analyzed by immunohistochemistry of inferior turbinate biopsies. The levels of total serum IgE and allergen-specific IgE antibodies in the serum were estimated by the PRIST and CAP RAST method, respectively. IL-13 gene expression was detected in the epithelial compartment of the nasal mucosa of 18/19 PAR patients but was undetected in normal volunteers and CIR patients.(ABSTRACT TRUNCATED AT 250 WORDS)