We identified a novel heterozygous single-nucleotide substitution 1400 T right curved arrow C (Leu 467 Pro) in the seventh exon of the interferon-gamma receptor 1 (IFNGR1) gene. This substitution was detected in 6 of the 89 allergic patients but not in the 72 non-allergic subjects. There was a difference in the L467P frequency between the allergic patients and the non-allergic subjects (Fisher's exact test: p=0.033). The 6 patients with L467P have allergic diseases such as bronchial asthma and/or allergic rhinitis. Furthermore, a familial analysis for L467P revealed a linkage between allergic diseases and L467P. Serum IgE levels of the patients with L467P were higher than those of the non-allergic subjects (p=0.001). Our previous studies have been shown that interferon-gamma (IFN-gamma) production by PBMCs in the allergic patients was lower than that in the non-allergic subjects. In this study, although IFN-gamma production in the allergic patients with L467P was equivalent to that in the non-allergic subjects, their serum IgE levels were high and they had allergic diseases. Our results suggest that some allergic patients have IFNGR dysfunction, and that L467P in the IFNGR1 gene is one of candidate susceptibility genes for allergic diseases.