Trypanosomes do not inhabit or grow in anopheles mosquitoes, the vector for the 
transmission of Plasmodium parasites the causative agent for malaria. The 
possession of lytic factors by the anopheline mosquito was thus considered. Head 
and midgut sections prepared in phosphate buffered saline were tested for 
trypanocidal action against T. congolense. While the head section was inactive 
towards the trypanosomes, the midgut extract at 0.2 mg ml(-1) diminished the 
motility of the parasites within 2 min of incubation; killing 50% of the 
population after 5 min. At 0.5 mg ml(-1) of the extract, about 90% of the 
parasites were killed within 2 min of incubation. The midgut fraction was 
subjected to a purification protocol involving successive chromatography on: 
octyl-sepharose, reactive brown agarose and fetuin-agarose columns. A final 
trypanocidal active fraction (gp45), which moved homogeneously during 
electrophoresis as a 45-kDa protein, was recovered from the fetuin-agarose 
column. The protein reacted positively with thiobarbituric acid, which suggests 
it is a sialoglycoprotein. Desialylation of the glycoprotein nullified its 
trypanocidal activity on T. congolense. Similarly, when the saccharides, 
lactose, methyl-beta-galactoside, lactulose, 
methyl-umbelliferyl-beta-galactoside (MU-Gal), were included in the culture 
medium, they inhibited the gp45 trypanocidal activity. Asialo-fetuin and 
asialo-RBC also inhibited the gp45-induced killing of T. congolense cells. The 
potential use of anopheline 45 kDa protein in the production of transgenic 
tsetse flies (Glossina spp.) in the control of trypanosomiasis is discussed.