o-Succinylbenzoic acid (OSB) is an intermediate in the biosynthesis of shikimatederived anthraquinones. The cell free activation of o-succinylbenzoic acid in extracts of anthraquinone producing cells of Galium mollugo L. is demonstrated for the first time. This activation depends on the presence of ATP, coenzyme A and Mg(2+). The o-succinylbenzoic acid coenzyme A ester was identified by converting it to 1,4-dihydroxy-2-naphthoic acid by a bacterial enzyme, viz. naphthoatesynthase. It is thus demonstrated that the o-succinylbenzoic acid coenzyme A ester derived from bacteria and from Galium mollugo cells are identical.