Chimeric histocompatibility genes encoding the amino-terminal (beta 1) domain of the class II Ak beta polypeptide and the carboxy-terminal (C2, transmembrane, and intracytoplasmic) domains of either the class I H-2Ld or H-2Dd molecules were stably introduced into mouse L cells. Although both were transcribed, only 5' Ak beta/3' H-2Dd transformants had significant cell membrane expression of a 30-40 kd, heterogeneous glycoprotein containing Ak beta 1 and H-2Dd (C2) serological epitopes. These transformants had a unique pattern of reactivity with monoclonal antibodies previously identified as requiring the Ak beta 1 domain for recognition of complete I-A molecules. These results allow new insight into the structural requirements for cell surface expression of proteins and provide unique cellular reagents for the dissection of humoral and cell-mediated recognition of MHC molecules.