Species of the Cupressaceae family are a worldwide cause of respiratory allergies. We used monoclonal antibodies (mAbs) to investigate the presence and the nature of cross-reacting epitopes shared by various components within Cupressus arizonica pollen extract (CaE) or by CaE and pollen extract from C. sempervirens (CsE). mAbs were produced in mice immunized with whole CaE (4A6 and 5E6) or with the major allergen components (2D5). Their reactivity was investigated by ELISA and immunoblotting before and after CaE periodate treatment. Cross-reactivity was evaluated by ELISA inhibition and immunoblotting. mAbs 2D5 and 4A6 recognized periodate-resistant epitopes, whereas the mAb 5E6 reacted with a periodate-sensitive determinant. The former mAbs recognized epitopes present on CaE major allergen and also shared by other components. mAb 5E6 showed a spread reactivity on CaE, with exclusion of the major allergen. When the three mAbs were tested with CsE, a restricted pattern of reactivity to mAbs 2D5 and 4A6 was obtained, whereas mAb 5E6 maintained a spread reactivity. The CaE major allergen is represented by two components recognized by human IgE and sharing common epitopes, as proven by mAbs reactivity. The use of these mAbs demonstrates that cross-reactivity within CaE components and between CaE and CsE is due to the presence of periodate-sensitive as well as -resistant epitopes.