This invention relates to novel nucleic acid molecules coding for opioid growth factor receptors. In particular, the present invention provides isolated nucleic acid molecules coding for human and rat OGF receptors. Antisense molecules, expression vectors and host cells, isolated proteins encoded by such nucleic acid molecules, antibodies directed against such proteins, as well as pharmaceutical compositions derived therefrom are also included. The invention further provides methods of modulating cell growth by using the isolated nucleic acid molecules, the antisense molecules and the antibodies directed against the encoded proteins.