We have used immunoblot analysis with glutathione and S-transferase fusion proteins as protein standards to examine expression of G alpha q/11 in membrane preparations from different organs and to assess changes during normal development. Adult rat tissues expressed 4-25 pmol/mg membrane protein G alpha q/11, with neonates expressing two to three times higher levels in several tissues (brain, heart, liver, and kidney). By contrast, levels of Gaq/11 in lung were similar in adults and neonates. A Gaq-specific antiserum confirmed the high expression in neonatal brain, heart, liver and kidney. Our results show that Gaq is developmentally regulated in many rat tissues.