Four gene products involved in the enzymatic synthesis of enterochelin from 2,3-dihydroxybenzoate, L-serine and ATP (Luke, R.K.L. and Gibson, F. (1971) J. Bacteriol. 107,557-562; Woodrow, G.C., Young, I.G. and Gibson, F. (1975) J. Bacteriol. 124, 1-6) have been partially purified using a previously reported fractionation procedure (Bryce, G.F. and Brot, N. (1972) Biochemistry 11, 1708-1715). The products of genes E, F and G have been separated from each other and correspond to the E1, E2 and E3 activities described by Bryce and Brot. These three gene products were not completely separated from the product of gene D. We refer to these gene products as components E, F, G and D of the enzymic apparatus for biosynthesis of enterochelin. Certain properties and functions of the four semi-purified components have been investigated. The E component is involved in the activation of 2,3-dihydroxybenzoate and the F component in the activation of L-serine. The D component physically associates with the F and G components during gel filtration and chromatography on DEAE Sephadex. It is proposed that the synthesis of enterochelin from L-serine and 2,3-dihydroxybenzoic acid is catalysed in vivo by a multienzyme complex, enterochelin synthetase.