Abstract Chalcone synthase from cell suspension cultures of Phaseolus vulgaris has been purified approximately 31-fold. The preparation formed the flavanone naringenin from malonyl-CoA and 4-coumaroyl-CoA. The P. vulgaris enzyme showed similarities to the enzyme recently purified from cell cultures of Petroselinum hortense with respect to molecular weight, pH optimum, ability to catalyse 14CO 2 exchange between NaH 14CO 3 and malonyl-CoA, and overall response of naringenin formation to varying thiol concentration. However, it appeared much less stable than the P. hortense synthase, exhibited significantly different apparent K m values for the two substrates and produced different ‘release products’ following purification. The enzyme was strongly inhibited by the isoflavanone phytoalexin kievitone, but not by isoflavone and isoflavanone precursors of kievitone. The possible relevance of the inhibition of the enzyme by phytoalexins is discussed.