The complexity of the phenolic constitution of flax tissues is demonstrated. A method for the purification of phenolic compounds and their estimation from a complex mixture of these substances in plant extracts is described together with the use of semi-micro paper chromatography and paper electrophorcsis for their identification. Chlorogenic acid and an isomer of this acid are shown to be present in four linseed varieties. The concentration of chlorogenic acid and the ratio of chlorogenic acid to total phenolics is studied in relation to disease resistance.