Antibodies raised against the T-beta gamma dimer of bovine retinal transducin specifically bind to the beta and gamma subunits of transducin in calf retina. Tissues from different vertebrates, but not from invertebrates, contained a band comigrating with the beta subunit of transducin (T-beta) which was immunostained. This protein most likely corresponds to the beta subunit of GTP binding proteins of hormonal systems (G-beta). In non-retinal vertebrate membranes, the antibodies did not recognize the gamma subunits of G proteins whereas a band comigrating with bovine T-gamma was detected in frog or rat retina. Although T-beta was precipitated by the T-beta gamma antiserum, we failed to immunoprecipitate the G-beta from calf brain.