We isolated and characterized the second major allergen (Cry j II) from Japanese cedar pollen. We found that most patients with this pollinosis had IgE antibody to this protein in addition to IgE antibody to Cry j I; however, some sera reacted only with Cry j I or Cry j II. IgE-ELISA inhibition studies revealed that Cry j I and Cry j II had no cross-allergenicity. Cry j II did not react with anti-Cry j I monoclonal antibodies. In SDS-PAGE under a non-reducing condition, Cry j II showed a band at the 37 kDa position, compared with the 45-50 kDa bands of Cry j I. N-terminal amino acid sequence of Cry j II was completely different from that of Cry j I.