Background: Aspirin/NSAIDs can release cysteinyl-leukotriene (cys-LTs) into airways and precipitate asthmatic symptoms in aspirin - induced asthma(AIA). It has been reported that there is profound overexpression of LTC4 synthase in their bronchial mucosa, compared to aspi- rin-tolerant asthma. Objective : We observed whether genetic polymorphism of LTC4 synthase may be predisposed to LTC4 synthase overexpression in AIA. Subject and method: Forty - four AIA patients having positive responses on lysin aspirin bron choprovocation tests and 47 non - aspirin induced asthma ( non - AIA ) patients having negative challenges and 32 healthy controls were enrolled. The genotypes of the promoter LTC4 synthase gene ( A,C transversion ) were determined by polymerase chain reaction and restriction frag- ment length polymorphism ( RFLP ) method. Results : LTC4 synthase promoter polymorphism ( A444C btransversion) was not significantly dif - ferent between non - AIA and AIA patients (p 〉0.05). Conclusion These findings suggest that genetic polymorphism of LTC4 synthase promoter may not be predisposed to LTC, synthase overexpression in AIA.