During fatty-acid biosynthesis, enoyl-acyl carrier protein (enoyl-ACP) reductase catalyzes the reduction of trans-2-enoyl-ACP to fully saturated acyl-ACP via the ubiquitous fatty-acid synthase system. NADH-dependent enoyl-ACP reductase (FabI) from Pseudomonas aeruginosa has been purified and crystallized as an apoenzyme and in a complex form with NADH and triclosan. Triclosan is an inhibitor of FabI and forms a stable ternary complex in the presence of NADH. The crystals of native and complexed FabI diffracted to resolutions of 2.6 and 1.8 Å, respectively. The crystals both belonged to space group P2(1), with unit-cell parameters a = 117.32, b = 155.844, c = 129.448 Å, β = 111.061° for the native enzyme and a = 64.784, b = 107.573, c = 73.517 Å, β = 116.162° for the complex. Preliminary molecular replacement further confirmed the presence of four tetramers of native FabI and one tetramer of the complex in the asymmetric unit, corresponding to Matthews coefficients (V(M)) of 2.46 and 2.05 Å(3) Da(-1) and solvent contents of 50.1 and 40.1%, respectively.