Rationale: While epidemiological studies have linked asthma susceptibility and severity to polymorphisms in human glutathione transferase Pi (GSTP)1, there is no direct evidence for a functional involvement of GSTP1 in processes that are pathognomic of asthma. Objectives: To examine the role of GSTP1 in modulating the development of allergic airways disease. Methods: Allergic airways disease was induced in WT and Gstp-null mice employing both acute and chronic models. Eosinophilia, goblet cells and remodeling were quantified by histological assessment, respiratory function was determined using invasive methods. ELISA was used to evaluate Th2 cytokines, eotaxin and phospho c-Jun. Gstp1/2 expression was quantified by RT-PCR. Results: Compared to allergic WT mice, eosinophilia, goblet cell hyperplasia, airway remodeling, lung resistance and IL-5 were enhanced in allergic Gstp-null mice. However, the protective efficacy of GSTP1 was mouse-strain dependent and associated with inherent variation in expression of Gstp1. Although elevated levels of phospho-c-Jun were detected in Gstp-null mice, treatment of WT mice with a GSTP/JNK inhibitory peptide enhanced phospho-c-Jun and significantly attenuated allergic responses. Conclusions: GSTP1 attenuates the severity of allergic airways disease. However, the efficacy of GSTP1 correlated with mouse strain-dependent variation in Gstp1 expression. Although GSTP1 attenuated c-Jun phosphorylation, treatment with a GSTP/JNK inhibitory peptide revealed an inverse relationship between c-Jun phosphorylation and allergic responses, indicating the mechanism by which GSTP attenuates allergic responses is not dependent on the JNK/c-Jun axis. Our data, together with epidemiological evidence, suggest variation in expression and/or function of this protein is an important determinant in asthma pathophysiology.