In order to determine whether the exsheathment patterns described in our previous study occurred in other microfilaria-mosquito systems, exsheathment of microfilariae of Brugia pahangi was studied in two species of mosquitoes. The results of the quantitative observation revealed that the microfilariae of Brugia pahangi tend to carry their sheaths into the haemocoel of Anopheles quadrimaculatus and Culex quinquefasciatus within 4 hr after infected blood meals. The percentage of the sheathed microfilariae in the haemocoel progressively decreased to 0% at 24 hr post-ingestion. Microfilariae remaining in the midgut of both species of mosquitoes were recorded most frequently casting off their sheaths in the midgut 2 hr post-ingestion. The percentage of microfilariae exsheathed in the midgut progressively increased to about 100% and 40% 24 hr post-ingestion in Anopheles quadrimaculatus and Culex quinquefasciatus respectively. These results confirm that exsheathment of microfilariae of Brugia pahangi occurs both in the haemocoel and in the midgut of two species of mosquitoes.