A study was conducted in 165 subjects with Japanese cedar pollinosis (JC) to evaluate the switching to the new standardized extract (SE) for patients who are going on specific immunotherapy (SP-IT) with conventional non-standardized extracts, products of Trii Co. or Hollister-Stier Co. Eight of 137 subjects exhibited adverse systemic reactions such as general skin eruption and despnea when JC allergen extract of Hollister-Stier Co. was switched to JC-SE. There were 6 cases where concentration of the extract had to be decreased due to extraordinary late reactions, while none of 28 subjects exhibited adverse side effect, when conventional allergen extract by Torii Pharmaceutical Co. was switched to JC-SE. Careful switching to high concentration of SE is required, because eight cases with adverse side effect were shown in switching to 200 JAU/ml and 2000 JAU/ml. 20 subjects started with SP-IT by JC-SE after spread of JC in the year of 2000 exhibited no adverse side effects in our protocol.