Attempts to generate reliable and versatile vectors for gene therapy and biomedical research that express multiple genes have met with limited success. Here we used Picornavirus 'self-cleaving' 2A peptides, or 2A-like sequences from other viruses^,,, to generate multicistronic retroviral vectors with efficient translation of four cistrons. Using the T-cell receptor:CD3 complex as a test system, we show that a single 2A peptide–linked retroviral vector can be used to generate all four CD3 proteins (CD3ε, γ, δ, ζ), and restore T-cell development and function in CD3-deficient mice. We also show complete 2A peptide–mediated 'cleavage' and stoichiometric production of two fluorescent proteins using a fluorescence resonance energy transfer–based system in multiple cell types including blood, thymus, spleen, bone marrow and early stem cell progenitors.