Many authors observed that mosquitoes respond to a large variety of artificial sounds (for references see Roth. 1948). Efforts to attract males of Aedes aegypti (L.) by play-back recoridings of the flight sound of the female have met with moderate success (Kahn et al., 1945; Offenhauser and Kahn, 1949; Kahn and Offenhauser, 1949). Roth (1948) demonstrated that males of A. aegypti approached the sounds of tuninh forks and sine sounds from a speaker. He also determined the upper and lower limits of frequencies that stimulated males, but in these experiments he did not use attraction to the source of the sound as the criterion of response, but the “seizing and clasping”reaction. He exposed the maIe mosquitoes in cages, three inches by three inches by one inch, placed against a box that housed a loud speaker. Under these conditions the mosquitoes had little opportunity to fly to orient themselves toward the sound source. Moreover the sound used was of such intensity (108 db at 2½ inches) that the whole cage vibrated, so that at least part of the response was undoubtedly caused by vibration of the substratum on which the mosquitoes rested. Sounds of such intensity do not normally occur in the natural environment of the mosquito. Moreover, the “seizing and clasping” response does not occur until the male approaches the female in response to sound or other stimulus. If the place of sound in the attraction of thc males is to be studied, the primary response, that of approach, should be the criterion and the amount of sound used should bear a reasonable relation to that occurring in nature.