Expression from a Drosophila metallothionein promoter (Mtn) was investigated in mosquito cells. Recombinant plasmids carrying a transcription unit comprised of the Escherichia coli beta-galactosidase gene (lacZ) fused to the metallothionein promoter were stably introduced into Aedes albopictus C6/36 cells. A low copy transformant containing approximately 60 copies of plasmid per cell, and a high copy transformant (1-2 x 10(4) copies/cell) were characterized. The expression of beta-galactosidase from the metallothionein promoter could be induced and controlled in this heterologous system, even when the copy number of introduced plasmid was several thousand.