The steady-state levels of mRNAs for the G-proteins G iα2, G oα, and the G β-subunits common to each were established in rat adipose, heart and liver. Uniformly-radiolabeled, single-stranded antisense probes were constructed from cDNAs or assembled from oligonucleotides. Direct comparison of the steady-state levels of the G-protein mRNAs was performed under identical assay conditions, and on a molar basis. In adipose, liver and heart, G sα mRNA was more abundant than mRNA for G oα, G iα, and G β. In adipose tissue, mRNA levels were as follows: 19.4, 7.6, 7.0, and 2.3 amol mRNA per μg total cellular RNA for G sα, G β, G iα2, and G oα, respectively. In heart G sα mRNA was less abundant than in adipose, but the relative trend among the G-protein subunits was the same. In liver, G β mRNA was more abundant than either G oα or G iα2. G oα mRNA levels ranged from 1.2 to 2.3 amol/μg total RNA in liver and adipose, respectively. The present work demonstrates the many advantages of this strategy when applied to the study of a family of homologous, low-abundance proteins and establishes for the first time the molar levels of G iα2, G sα, G oα, and G β-subunit mRNAs in several mammalian tissues.