Toxicity of malathion mixed with diluents was examined for boll weevil. Topical application test included an acetone standard, paraffinic oil, crude cottonseed oil and once refined cottonseed oil. The addition of acetone to malathion and paraffinic oil was required to obtain a satisfactory mixture. Malathion was diluted in the cottonseed oils without acetone. Toxicity of malathion in paraffinic oil was significantly greater than shown for any of the other diluents. With the discovery of a field stable formulation it could be possible to reduce the use of malathion in Boll Weevil Eradication Program. This could lead to a substantial cost savings and reduced environmental impact.