Thiamine-(14)C moved through petiolar sections of Lycopersicon esculentum Mill. var. Michigan State Forcing with striking similarity in kinetics to auxins and gibberellic acid moving through similar sections of other green plants. Thiamine moved with strong basipetal polarity, at a velocity of 3 to 5 mm per hour, and emerged unchanged into the basal receiver agar block, judging by chromatography. This lends support to the hypothesis that polar movement is a property of several classes of plant hormones, rather than being restricted to the auxins (as previously believed).