The distribution and levels of expression of Gs-alpha, Gil-alpha, Gi2-alpha, Gi3-alpha, Go-alpha, and Gx-alpha mRNAs were compared by Northern blot analysis using several rat tissues and selected human and rat cell lines. Gi1-alpha, Go-alpha, and Gx-alpha, were detected in a limited number of tissue and cells whereas Gi2-alpha, Gi3-alpha, and Gs-alpha, were expressed in all the tissues and cells tested albeit in varying amounts. The expression of these six genes appears to be differentially regulated during postnatal development of the rat brain. High expression levels particularly of Go-alpha, in young rat brain may be related to the formation of neurites during differentiation of nerve cells.