This paper describes a novel surface-processing technique aimed at the in vivo formation of ordered functionalized structures on surfaces. The essential feature of this technique is the utilization of an intrinsic and stable two-dimensional crystal of bacteriorhodopsin (bR) as a template. A simple technique to form a functional chimera of the halophilic enzyme dihydrofolate reductase (hDHFR) with bR is demonstrated. The gene encoding hDHFR from Haloferax volcanii (H. volcanii) was conjugated to that encoding bR (bop) from Halobacterium salinarum (H. salinarum). This chimera was expressed in a bop-deficient strain of H. salinarum. The novel bifunctional fusion protein bR-hDHFR was localized in the plasma membrane of H. salinarum and retained the intrinsic characteristics of each component. Microscopic patches composed of ordered bR-hDHFR molecules were observed on the plasma membrane by electron microscopy. The hDHFR portion of the chimera was detected on the cytoplasmic side of each patch, which confirms that the molecular orientation of the fused proteins was vectorially controlled. The molecular packing of the fusion protein closely resembled the ordered structure of the wild-type bR in the "purple membrane". which forms a two-dimensional crystal. This technique for the immobilization of functional proteins on a surface is applicable to a wide range of proteins for organizing ordered supramolecular surfaces on the nanometer scale.