The formation of penicillinase by cultures of Bacillus licheniformis was preferentially suppressed by cerulenin, an antibiotic known to specifically inhibit fatty acid synthesis in microorganisms. The effect was studied at cerulenin concentrations that had almost no effect on the rate of cell growth and overall protein synthesis, but that reduced the rate of [14C]acetate incorporation (by 50 to 70%), indicating partial inhibition of lipid synthesis. The levels of both the released enzyme (exopenicillinase) and its cell-bound precursor were reduced to the same extent (70% to 80%). Enzyme formation was gradually resumed after the removal of cerulenin or the addition of a mixture of fatty acids prepared from lipids extracted from B. licheniformis. Reversal was less effective as the time interval between treatment with cerulenin and addition of fatty acids increased. We conclude that de novo synthesis of fatty acids is required for the formation of both the membrane-bound and extracellular penicillinase. Suppression of the membrane-bound enzyme is a likely consequence of the altered membrane (decreased lipid-to-lipid ratio and increased density) seen in cerulenin-treated preparations. The corresponding suppression of exopenicillinase is consistent with the view that it is derived from the membrane-bound form. A mechanism linking the general class of exportable proteins to specific aspects of lipid synthesis is discussed.