Methods and uses are described for treating or preventing diseases of humans or non-human animals by reducing the amount of active leukotriene B.sub.4 (LTB.sub.4) in those in need of such treatment using LTB.sub.4 hydroxylases. In certain embodiments, LTB.sub.4 hydroxylase is administered in combination with nicotinamide adenine dinucleotide phosphate and/or an NADPH-cytochrome P-450 reductase. The invention is particularly useful for treating or preventing respiratory diseases that are caused or exacerbated by inflammation.