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Abstract: Fexofenadine, an antihistamine drug used in allergic rhinitis treatment, can be produced by oxidative biotransformation of terfenadine by Streptomyces platensis, which involves three consecutive oxidation reactions. We report here the purification and identification of the enzyme responsible for the first step, a cytochrome P450 (P450)-dependent monooxygenase. The corresponding P450, designated P450 terf , was found to catalyze the hydroxylation of the t-butyl group of terfenadine and exhibited UV–Vis characteristics of a P450. Its interaction with terfenadine led to a shift of its Soret peak from 418 to 390nm, as expected for the formation of a P450–substrate complex. In combination with spinach ferredoxin:NADP(+) oxidoreductase and ferredoxin, and in the presence of NADPH, it catalyzed the hydroxylation of terfenadine and some of its analogues, such as terfenadone and ebastine, with km values at the μM level, and kcat values around 30min−1. Sequencing of the p450 terf gene led to a 1206bp sequence, encoding for a 402 aminoacid polypeptide exhibiting 56–65% identity with the P450s from the 107L family. These results confirmed that P450s from Streptomyces species are interesting tools for the biotechnological production of secondary metabolites, such as antibiotics or antitumor compounds, and in the oxidative biotransformation of xenobiotics, such as drugs. [Copyright &y& Elsevier]