Evidence that β-alanine or calcium pantothenate partially reversed the inhibitory action of several chlorinated aliphatic acids on yeast growth (4) suggested the hypothesis that synthesis of pantothenate is one of the metabolic pathways sensitive to this group of herbicides. The objectives of the experiments reported herein were (a) to determine the mechanism by which the enzymatic synthesis of pantothenate was inhibited by these compounds, (b) to seek evidence for the contributions of this mechanism, in vivo, to the herbicidal effects of 2,2-dichloropropionic acid (dalapon), (c) to determine whether pantothenate treatments could overcome the effects of dalapon in plants and (d) to test chloro-substituted analogs of pantoate for herbicidal activity. To achieve the last objective it was necessary to synthesize several new chemicals.