The Mariana Islands lie well within the vast "malaria-free" region of the central and south Pacific Ocean. However, Anopheles indefinitus was discovered on Guam in 1948, and an additional four species of Anopheles were collected on the island during 1970-75. Early malaria cases on Guam were diagnosed as relapsing infections with the disease having been contracted in other areas. Small outbreaks of malaria were recorded on Guam in 1966 and 1969, and autochthonous cases were indicated in both. Since vector capability for malaria does exist on Guam, quarantine procedures at the air and seaports combined with public health disease surveillance and an integrated anopheline control program are recommended for the island.