Field studies were made to determine the concs. of hexachloro-cyclohexane necessary for practical commercial control of Limonius agonus on potatoes. Excellent commercial control, <6% out of Grade IT. S. 1, was obtained by the application per acre of at least 1.5 lb. crude material, containing 10% of isomer in the row before planting or 2 to 2 1/2 lbs. broadcast in a grain drill and disc harrowed twice. Seedpiece treatment, both as a dust and a dip, was reasonably effective and poison baits, 1-1000 by wt. in wheat, showed little practical effect. Taste in tubers resulted from the application per acre of <1 lb. of crude material in the row or 2l/2 lbs. broadcast on fine sandy loam soils with a reaction of pH 5.