OBJECTIVES: Allergen is closely related with local features and cultural environment and a new approach method regarding causes triggering aggravation is especially required due to complex and variety of ordinary residence and pollution of living environment recently. We, therefore, performed this study to inspire the necessity of identification of causative afeuts in aothmatic patients in pusan area. METHODS: We measured serum specific IgE antibody by means of chemiluminescent analyzer employing MAST, classified the level from class 0 to 4 and interpreted the result in order to identify allergen on total 262 patients consisted of inpatients and outpatients who had been presumed as extrinisic asthma and treated in this hospital during 2 and a half years from June of 1994 to December of 1996. RESULTS: 1. With regard to sex and age distribution, the rate of men versus women was 1 : 1.3, while in the distribution by age, the twenties and the thirties were the most as 29% and 26% respectively. 2. The result of interpretation of the test showed positive in 75%, 78% of which showed positive reaction compounded of 2 kinds or more. 3. If we take a look at the distribution of total IgE class in the positive area, we can find that ; Class III and class II showed the highest frequency as 47% and 37% respectively. 4. If we take a look at the distribution by age and allergen, the twenties(32%) and the thirties(30%) showed the highest frequency, the fifties, the forties and the teens showed middle frequency as 10~13% and the sixties and the seventies showed the lowest frequency as about 1%. The causative allergen appeared in the order of pollen(40%), dust(20%), food(18%), fungus(13%) and epidermis(8%). 5. The distribution of allergen by season generally showed high rate of positive appearance in spring and fall as pollen appeared in spring(44%) and fall(27%), dust appeared in fall(32%) and summer(23%), food appeared in spring(34%) and fall(29%), fungus appeared in fall(30%) and spring(28%) and epidermis appeared in spring(30%) and fall(28%). 6. With regard to the allergen: (1) In pollen allergens, trees showed higher positive frequency than weeds and trees were in the order of birch(14%), alder(13%) and hazelnut mix(12%) and weeds showed similar positive values. (2) In dust allergens, mite(D. pteronyssinus and D. farinae) showed high positive rate as 39% each. (3) In epidermal allergens, it also showed relatively even positive value among which cat's halr-dandruff was the highest as 40%. (4) In food allergens, shrimp showed the highest as 22% and others were similar as evenly positive values. (5) In fungus allergens, Candida and Stemphylium showed the highest value as 19% each. CONCLUSION: The analysis of allergen by means of MAST could be used as a valuable guide post for identifing cousative antigens for active treatment of extrinsic asthma.