Saliva was collected from females of Boophthora erythrocephala (Simulium erythrocephalum) and Wilhelmia lineata (S. lineatum) as they were feeding on a saline-ATP solution through an artificial silicone membrane. The histamine content of the saliva was measured by high-performance liquid chromatography (HPLC). The amount of histamine salivated by B. erythrocephala (2.9 ng/individual when feeding to repletion) was more than four times that released by W. lineata (0.7 ng/individual). For both species, the quantity of histamine salivated increased with duration of feeding and partially with the age of females. The proportion of histamine retaines by in vitro fed W. lineata averaged 36.1% W. lineata females engorged on saline-ATP solution, or stimulated for feeding with the same medium, produced significantly more hist-amine than died unstimulated flies.