BACKGROUND: Hop Japanese (Hop J) pollens are abundant in the air of Korea during the autumn season. Their significances as a source of allergenic sensitization have been underestimated in this country. MATERIAL AND METHOD: In other to observe clinical features of Hop J-sensitive asthmatic patients in this country, skin prick test with Hop J pollen was performed. The serum specific IgE antibodies to Hop J pollen antigen were detected by enzyme linked immunosorbent assay (ELISA) in positive responders (>2+ of A/H ratio) on skin prick test. To confirm the respiratory sensitization, bronchoprovocation test was performed in 17 asthmatic patients sensitive to this pollen. RESULT: Ten asthmatic subjects showed a significant bronchoconstriction following the inhalation of Hop J pollen extract (6 early and 4 dual astmatic responses) and all of them had high serum specific IgE bindings, with minimal bindings in negative responders. They have suffered from seasonal aggravation of asthmatic symptoms with or without rhinitis, and/or conjunctivitis symptoms. The skin reactivity to Hop J had more than 5+ of A/H ratio on skin prick test in nine positive responders, whlie negative responders showed from 1+ to 3+ response. Moreover, four (40%) asthmatic subjects showed a positive response to only the Hop J pollen on skin prick test and an isolated positive asthmatic response to the Hop J bronchoprovocation test. CONCLUSION: We believe that the Hop J pollen should be considered as an allergen during the Autumn season, and thus included in skin test batteries in this area. Some labelled having intrinsic asthma or rhinitis might be sensitized to this pollen or other unknown allergens.