The behavior of HCN gas under a form tent over an orange tree has been studied. The distribution of the gas was detd. both with methods of liberation now in practice and with methods that have been discarded. It was found that all the methods produced locations of low cone, especially near the periphery of the tent. The cone, of the gas varied sufficiently to produce significant differences in mortality of scale insects. A method has been developed to reduce this variation by first diluting the HCN with air by means of a blower inside the tent. This improvement is supported by chemical analyses and by the tests of mortality of scale insects placed at several locations in the tent. Adequate distribution of the gas was also obtained with the dilution device when trees in a lemon grove were covered with regular fumigation tents.