Latex allergy is a recently increasing hazard to people who are repeatedly in contact with Latex products. Notably, with this allergy, cross‐reactivity to vegetable foods and pollen is frequently observed. It is postulated that pathogenesis‐ or, rather, defence‐related proteins induced in rubber trees are responsible for the Latex allergy and the cross‐reactivity. To evaluate this hypothesis, an esterase was selected as one of the probable defence‐related proteins in rubber Latex and its involvement in Latex allergy was investigated. The biochemical properties of a chromatographically purified esterase from ammoniated Latex were compared with those of esterases (hevains) previously purified from rubber Latex. The antigenicity of the esterase was examined by immunoblotting using sera from Latex‐allergic patients. The purified esterase (of molecular weight 80 kDa) dissociated into subunits under denaturing conditions and shared biochemical properties with hevain1from lutoids. The esterase was recognized by IgE in patients’ sera. This suggests the relevance of the purified esterase to Latex allergy.