Beginning in 1945 with DDT residual spraying dramatic success was achieved in elimination of malaria from the former British Guiana. Anopheles darlingi and malaria were eliminated from the coast by 1951, but limited numbers of cases continued to be found in the interior. The Mosquito Control Service of the present Cooperative Republic of Guyana has been unable to control the deterioration of the situation in the interior, especially in 4 of the country's 48 operational sectors which have more than 80% of the cases. High densities of An. albitarsis (now correctly recognized as An. braziliensis) have been found, and a broad range of entomological studies of this and other Anophelines is urgently needed, along with a more intensively conducted residual spraying program to determine objectively the effectiveness of this measure.