Leukotriene (LT) B₄ is an inflammatory mediator that has been implicated in the pathogenesis of various diseases, including inflammatory bowel disease and psoriasis. As the rate-limiting step for LTB₄ production, LTA₄ hydrolase represents an attractive target for therapeutic agents that interfere with LTB₄ production. In the present study we evaluated a chemically novel compound designated SC-57461A (3-[methyl[3-[4-(phenylmethyl)phenoxy]propyl]amino]propanoic acid HCl) as an inhibitor of LTA₄ hydrolase. Pharmacological comparisons are made to its free acid SC-57461. SC-57461A is a potent competitive inhibitor of recombinant human LTA₄ hydrolase when either LTA₄(IC₅₀ = 2.5 nM, K _i = 23 nM) or peptide substrates (IC₅₀ = 27 nM) are used. In human whole blood, the IC₅₀ for calcium ionophore-induced LTB₄ production was 49 nM, indicative of good cell penetration. Whole blood production of the cyclooxygenase metabolite thromboxane B₂ was not affected. SC-57461A was also active in several other species, including mouse, rat, dog, and rhesus monkey. The data indicate that SC-57461A is a potent and selective inhibitor of LTA₄ hydrolase.