Guarding against the introduction of diseases from other countries is a responsibility of the Division of Foreign Quarantine of the U. S. Public Health Service. The Service has been charged with this duty since 1798. Control measures against Aedes aegypti mosquitoes became an accepted Public Health procedure on ships with the discovery in 1900 of the relationship of this mosquito with the yellow fever virus. However, it was not until the early days of international air travel that Public Health quarantine entomology as such, had its inception. Even in these early days epidemiologists of the Service foresaw an era in which there would be increased dangers to our country through the possible importation of insects from foreign countries by airplane. Their realization of this potential threat to our country led to the first reported studies of insects on aircraft. Griffitts (1931) inspected 102 aircraft arriving at Miami, Florida, from Central and South America and the Caribbean area during 1931 and reported the occurrence of 29 mosquitoes on 21 planes. This observation posed a logical question. Can insects survive at the high altitudes and cold temperatures in which planes fly? Subsequent tests by Griffitts (1933) demonstrated the ability of mosquitoes to survive for approxiinately 80 hours of flying time and at 14,000 feet altitude in these prototypes of the modern plane. Carnahan (1938) reported on insects recovered from aircraft at Miami, Florida, while Welch (1939) was the only worker up to that time to pay any attention to insects other than those of medical importance. Denning et al. (1947) and Hughes (1949) have admirably summarized the findings made by Public Health Service inspectors. Since those days much has been said of the accidental transport of insects in aircraft. Observations made today indicate that live insects, including mosquitoes, are frequently found on the modern planes which fly at higher altitudes and often for greater lengths of time than the early planes. The knowledge that mosquitoes were able to survive at the altitudes these early planes sometimes reached in their international flights was cause for deep concern. It could have been pigeon-holed as just another observation in the gathering of scientific information, but, remembering the not too far removed outbreak of yellow fever in New Orleans, our officials were not anxious to allow foreign mosquitoes access to our shores. The development of heated and pressurized cabins further increased the possibilities of transporting live mosquitoes. Consequently, studies were commenced to find the best way to prevent these insects from establishing themselves in this country. The earliest control measures made use of hydrocyanic acid gas fumigations, rotenone dusts and formaldehyde sprays, but none of these were