Foot-and-mouth disease virion RNA is translated efficiently and completely in a rabbit reticulocyte lysate cell-free system. Treatment of cell-free lysates with monospecific serum prepared against the individual viral structural proteins or with monoclonal antibodies prepared against the inactivated virus or against a viral structural protein precipitated all of the structural proteins, suggesting that structural protein complexes were formed in vitro. Sucrose gradient analysis of the cell-free lysate indicated that complexes sedimenting at 5, 14, 60 to 70, and ca. 110S were assembled in vitro. Structural proteins VP0, VP1, and VP3 were the major polypeptides found in these complexes. The material sedimenting at 110S, i.e., containing VP0, VP1, and VP3, was precipitated by a 140S-specific monoclonal antibody but not by a 12S subunit-specific monoclonal antibody, suggesting that this capsid structure contained at least one epitope present on the intact virus.