A rational method for constructing highly oriented films of purple membrane (PM) has been established by using two kinds of bispecific antibodies with different antigen-binding sites, one binding to a specific side of bacteriorhodopsin and the other to a phospholipid hapten. A hapten monolayer deposited on a metal electrode was treated with a bispecific antibody solution and incubated with a PM suspension to produce a highly oriented PM film, as confirmed by electron microscopy in which an immunogold labeling technique was used. This antibody-mediated PM monolayer was then used in the construction of a light-sensing photoelectric device. A comparison of the two incorporated PM monolayers showed that highly efficient photocurrents were produced by the PM monolayer whose unidirectionally oriented cytoplasmic surface faces the electrode.