Glutamyltranspeptidase binding (G) proteins play an important role in intracellular signal transduction downstream from many receptors, including opioid receptors. Moreover, it was recently reported that the beta-subunits of G proteins, in addition to the alpha-subunits, regulate effector pathways. In this study, membrane G protein immunoreactivity was estimated by Western blotting with polyclonal antibodies (RM/1, AS/7, GC/2, QL, and SW/1) against specific G proteins (G alpha S, G alpha i-1,2, G alpha o, G alpha q, and G beta, respectively) in postmortem temporal cortex obtained from 6 heroin addicts and 6 control subjects without a history of drug abuse. Immunoreactivities of the G beta-subunit increased significantly (p < 0.05) in heroin addicts, compared with controls, and that of G alpha i-1,2 tended to increase in heroin addicts. Present findings suggest that the alterations in G protein-mediated signal transduction may be involved in the mechanism of opiate addiction.