We have developed plasmid and phage vectors for the display of foreign proteins on the surface of bacteriophage lambda capsid by modifying the D gene which encodes the major head protein gpD. The vectors have multiple cloning sites, and permit colour selection and conditional chain termination for recombinants. Displayed proteins can be fused to either the N or C terminus of gpD by a peptide linker. The conditional chain termination scheme, via a host Escherichia coli suppressor activity, allows the fusion and assembly of homomultimeric proteins as well as control of the number of fusion proteins per phage particle. We have successfully displayed beta-lactamase, IgG-binding domains of the Staphylococcus aureus protein A, and beta-galactosidase by cloning the genes into the vector. The constructs express functionally active proteins fused to gpD that assemble into phage particles. These results suggest that gpD may be fused to many other peptides and proteins at their N or C terminus and the fusion products may be accessible on the surface of bacteriophage lambda particles.