The RNA encoding the alpha subunit of the G(o) GTP-binding protein is alternatively spliced in some tissues to produce mRNAs encoding two distinct forms of the protein which differ at the carboxyl terminus. This alternative splicing process is observed at all stages during development of the rat brain and heart and in some but not all neuronal cell lines. These effects are discussed both in terms of the regulation of the alternative splicing event and the functional role(s) of the two forms of the protein which it produces.