SUMMARY1The relation of this investigation to other problems connected with wood fumigation is indicated and previous work bearing on the subject is reviewed.2The technique is described by which the toxicity of hydrocyanic acid gas to certain wood‐feeding insects has been determined under standard conditions.3Results of experiments withLyctussp. larvae at 20 and 25° C. and withLyctus brunneusbeetles andAnobium punctatumlarvae at 25° C. are given and resistance curves for different concentrations and exposures drawn from them.4The relative resistances and the toxicity relationships of the different insects are discussed.5Experiments withLyctuslarvae at 20 anu 25° C. show that the insects are more susceptible to HCN at the higher temperature.6At 25° C.Lyctuslarvae are more susceptible to HCN thanLyctusbeetles orAnobiuml