We reported here 53 cases of birch pollen nasal allergy treated in our department from 1990 to 1991. The 53 patients constituted 16% of 335 total nasal allergy patients. In recent years, the number of birch pollen nasal allergy patients has apparently been gradually increasing in Sapporo. Skin tests, radioallergosorbent test (RAST) determinations and nasal provocation tests were performed for the diagnosis of birch pollen nasal allergy, and high degrees of correlation were observed among these tests. Therefore, it seems to be reasonable to determine the birch pollen allergy with only a positive case history of early springtime hay fever and RAST determination. A high correlation coefficient (Rho) value was found with RAST determinations between birch pollen and alder pollen. Furthermore, RAST of alder pollen was significantly inhibited by birch pollen extracts. These results indicate cross reactivity, presumably due to partial immunologic identity between these two pollen allergens.