BACKGROUND: Drug-induced pulmonary toxicity is a serious and expanding problem with often unknown aetiology. Many drugs are metabolized by cytochrome P450 (CYP) enzymes. OBJECTIVE: To establish whether allelic variation in CYP polymorphic genes contributes to variability in drug response and unexpected toxicity. METHODS: A case-control study was conducted. The cases consisted of patients with drug-induced interstitial lung disease (DI-ILD; n = 59). Two control groups were used: one group of healthy volunteers (n = 173) and one group of patients with idiopathic pulmonary fibrosis (IPF; n = 110). RESULTS: Of the patients with DI-ILD 91.5% (54/59) had at least one of the studied variant genes compared with 70.5% (122/173, p < 0.001) of the ...