The beta-subunit of the high-affinity IgE receptor (Fc epsilon RI-beta) on chromosome 11 is maternally linked to atopy, the state of enhanced IgE responsiveness underlying allergic asthma and rhinitis. We have identified a common variant of Fc epsilon RI-beta, lle181Leu within the 4th transmembrane domain. Leu181 shows significant association with positive IgE responses in a random patient sample. Amongst 60 unrelated nuclear families with allergic asthmatic probands, Leu181 is identified in 10 (17%), is maternally inherited in each, and shows a strong association with atopy. Our data indicate that Fc epsilon RI-beta, subject to maternal modification, may be the atopy-causing locus on chromosome 11q.