Pretreatment of pea (Pisum sativum var. Alaska) sections with any active auxin induces an enzyme which forms aspartate conjugates of exogenously supplied indoleacetic acid, naphthaleneacetic acid, or benzoic acid. Whereas induction of this system is an absolutely auxin-specific process, another enzyme, which forms benzoylmalic acid, is induced both by auxins and by physiologically inactive aromatic carboxylic acids. Induction of both enzymes is abolished by low levels of RNA and protein synthesis inhibitors. The induction specificities and other characteristics of the two systems are compared.