A degenerate PCR strategy was used to isolate a fragment of the acetylcholinesterase gene (Ace) homolog from Aedes aegypti and screen for a cDNA clone containing the complete open reading frame of the gene. The predicted amino acid sequence of the Aedes gene shares 64% identity with Ace from Drosophila and 87% identity with the acetylcholinesterase gene from another mosquito species Anopheles stephensi. High levels of expression of the Aedes gene were achieved by infection of Sf21 cells with a recombinant baculovirus containing the Aedes Ace cDNA. The catalytic properties and sensitivity of the recombinant enzyme to insecticide inhibition are described and discussed in relation to the role of insensitive AChE in conferring resistance to organophosphorus and carbamate insecticides.