The mode of action of different insecticides used against dry wood insects and the correlation between their thresholds and the commercial formulations in which they are used are considered in the light of laboratory test results. Though a parallel can be drawn between these toxic values and commercial formulations with preventive action, the same relation is not found with eradicant action. It seems that the toxicity of active ingredients is not the only factor to be taken into account. Beyond a certain point, the efficacy is not necessarily proportional to the amount of insecticide used.