To evaluate the role of gamma delta T cells in atopic asthma, we examined the relationship among atopy bronchial asthma, and genetic polymorphism of the gamma chain of T cell receptors (TCR) in families through atopic asthmatic probands. We recruited 5 families (69 subjects). Total serum IgE levels were estimated by a radioimmunosorbent test (IgE RIST). Skin prick tests were done with inhaled allergens consisting of house dust, grass and tree pollens, common molds, and animal danders. Antigen-specific IgE levels in response to these allergens were also measured by multiple antigen simultaneous test (IgE MAST). The atopic phenotype was determined by the presence of a positive skin test, an elevated antigen specific IgE value, an elevated total IgE level, or some combination of these. Although linkage of atopy or bronchial asthma to the gene encoding the gamma chain of TCR was excluded, the lod score between this gene and molds-specific IgE responses was 0.42 at the recombination fraction of 0.1. In an association study, a 19 kb allele of the gamma chain of the TCR gene was found more frequently in asthmatic subjects than in non-asthmatic subjects (p = 0.068). Also, molds-specific IgE responses were significantly associated with this allele (p = 0.018). These findings suggest that molds-specific IgE responses underlying atopic asthma are partly regulated by the gene encoding the gamma chain of the TCR.