Bacteriophage lambda (lambda) permits the display of many foreign peptides and proteins on the gpD major coat protein. However, some recombinant derivatives of gpD are incompatible with the assembly of stable phage particles. This presents a limitation to current lambda display systems. Here we describe a novel, plasmid-based expression system in which gpD deficient lambda lysogens can be co-complemented with both wild-type and recombinant forms of gpD. This dual expression system permits the generation of mosaic phage particles that contain otherwise recalcitrant recombinant gpD fusion proteins. Overall, this improved gpD display system is expected to permit the expression of a wide variety of peptides and proteins on the surface of bacteriophage lambda and to facilitate the use of modified lambda phage vectors in mammalian gene transfer applications.