Retroviral vectors are used widely in research and are also being designed for use in gene therapy trials. In practice, these vectors usually contain a marker gene, which is often a drug selection gene. In this report, a novel retroviral vector has been constructed which contains a gene that allows selection for infected cells by a magnet. This gene is a single-chain antibody (sFv) to a specific hapten molecule 4-ethoxymethylene-2-phenyl-2-oxazolin-5-one (phOx). sFv specific for phOx is displayed on the surface of infected cells. This feature allows binding to phOx-BSA coated magnetic beads which are used to isolate the infected cells.