Small-scale laboratory tests against Sitophilus oryza in wheat were conducted with piperonyl butoxide alone, pyrethrins alone, and with combinations of these 2 materials in dusts to determine the degree of synergism between pyrethrins and piperonyl butoxide. Piperonyl butoxide used alone at the dosages listed was almost completely ineffective against the rice weevil. Pyrethrins alone at dosages 10-20 times those used in the combinations-gave from moderate to good control. Combinations of the 2 materials in 4 different ratios gave from good to complete control over the 30-day test period. An empirical method for calculating "total concn." is described. Dusts with 4 ratios of piperonyl butoxide and pyrethrins, but having the same calculated "total concn." of active ingredients, were approx. equal in effectiveness. It is concluded that marked synergism between piperonyl butoxide and pyrethrins can be demonstrated against the rice weevil, and that this synergism is operative over a wide range of ratios of the 2 materials.