At the time of writing, 1949, field work on mosquitoes has been carried on in Bwamba County, western Uganda, for a period of ten years, with very few intermissions. The topography and vegetation of this area have been described elsewhere (Haddow, 1945a). The main effort has centred round the search for forest vectors of yellow fever, but much work has also been done in native plantations, huts, etc. While genera such asAëdes and Taeniorhynchus have, inevitably, required special attention, records of all mosquitoes encountered have been kept throughout the investigation, whether or not they seemed likely to be involved in the local epidemiology of yellow fever. Certain sections of the work have already been published (Mahaffy & others, 1942; Haddow, 1945a, 1945b, 1945c, 1946 and 1948; Haddow & others, 1947; Haddow & Dick, 1948; Haddow & Mahaffy, 1949), but a great part of it has not as yet been submitted.