Two electronic devices emitting sound waves which, according to label and advertised claims, ward off most female mosquitoes, for a distance of 0.9 to 2.5 ms (3-8 ft) were tested to ascertain their effectiveness as mosquito repellents. Evaluations were conducted in a chamber under practical-use conditions as defined by Soltavatta (1947) to be a distance of 10 in. The results of all evaluations indicated that the devices did not afford protection against the bites of Aedes aegypti mosquitoes as claimed by the manufacturer under the conditions used in this study. Only one species of mosquito was used in this study because it has been observed by Soltavatta (1947) that the flight sound pitch is practically the same for all species of mosquitoes.