A method is described for the micro-identification of both mono- and diesters of 12-deoxyphorbol based upon a combination of thin-layer chromatography and mass spectrometry. The technique may be used on as little as 5 ml of fresh plant latex. Nine thin-layer systems are described, six of which are adsorption systems based on silica gel or alumina as adsorbent, and three are partition systems using diethyleneglycol as stationary phase. The migration by means of thin-layer chromatography is dependent upon the chain length of the C-13 esterifying acid and on the presence or absence of a free primary hydroxyl group at C-20. By means of mass spectrometry it was possible to confirm the identity of the esterifying moiety at both the C-13 and C-20 positions of 12-deoxy-4βOH-phorbol.