Phlebotomine sand fly populations were studied over a one year period by light-trap collections along a 200 m transect at Empire Range, Panama Canal Zone. The zoophilic speciesLutzomyia carpenteri(Fairchild and Hertig) was dominant during the dry season while the anthropophilic speciesL. panamensis(Shannon) was dominant during the wet season. Sand fly populations were strongly correlated with the degree of development of the forest cover, increasing from grassy to secondary forest biotopes and from secondary forest to mature forest biotopes.