OBJECTIVE: The ATP-binding cassette transporter ABCC1 [i.e. multidrug resistance-associated protein 1 (MRP1)] is a membrane-bound pump excreting a variety of xenobiotics from the cell, and thus ABCC1 may play an important role in smoking-related lung function loss and development of chronic obstructive pulmonary disease (COPD). We earlier showed that bronchial epithelium of COPD patients have lower ABCC1 expression than that of healthy controls, with even further decrements in more severe COPD stages. In line with these results, we now aimed to assess effects of ABCC1 single nucleotide polymorphisms (SNPs) on both the level and the longitudinal course of lung function in the general population. METHODS: All 51 prevalent (minor allele frequency >5%) and noncorrelated (r