A mouse major histocompatibility antigen (H-2) gene, encoding a novel H-2Ld molecule lacking its intracytoplasmic domain, has been constructed and introduced into mouse L-cells. The novel H-2 molecule is found on the surface of the transfected cells at the same level as L-cells transfected with the native H-2Ld gene. Allo- and influenza-specific cytotoxic T lymphocytes can recognize the truncated H-2 gene product nearly as efficiently as the normal H-2Ld gene product. However, vesicular stomatitis virus-specific cytotoxic T lymphocytes recognize the truncated H-2Ld molecule less efficiently than the complete H-2Ld product. The rate of capping of the truncated H-2Ld molecule was investigated and found to be the same as that of the complete H-2Ld gene product.