The efficacy of Arosurf MSF alone and in combination with three preparations of Bacillus thuringiensis var. israelensis (B.t.i.) against Anopheles albimanus larvae, pupae and eggs was determined by bioassay. Arosurf MSF alone was effective against the egg, 4th larval instar and pupal stages. All Arosurf MSF and B.t.i. combined formulations produced over 90% mortality of all larvae and pupae, 48 hr posttreatment. Egg eclosion was reduced to approximately 25% with all formulations containing Arosurf MSF.