Aging has been associated with alterations in signal transduction for a number of neurotransmitter receptors in human tissues. Heterotrimeric G proteins play a pivotal role in postreceptor information transduction, by coupling a variety of hormone and neurotransmitter receptors to several intracellular effector functions. Developmental and age-related changes in the abundance of specific G alpha subunits have been shown in the human brain. In the present study, functional and quantitative measures of G proteins were conducted in human mononuclear leukocytes obtained from 19 healthy subjects of increasing age. Gs protein function, assessed through cholera toxin-sensitive beta-adrenergic and dopaminergic agonists induced increases in 3H-Gpp(NH)p binding capacities to membranes of mononuclear leukocytes, and Gi protein function, assessed through pertussis toxin-sensitive muscarinic agonist induced increase in guanine nucleotide binding capacity, were found to be unaltered by increasing age. Immunobloting analyses with specific polyclonal antibodies against G alpha s, G alpha i, and G alpha q subunit proteins in mononuclear leukocyte membranes obtained from the same subjects showed that the quantities of these proteins in mononuclear leukocytes were as well independent of age. Insofar as age-related alterations in cellular information transduction mechanisms in peripheral tissues are important from the etiological, diagnostic, and pharmacological aspects of age-related disorders, it is important to know that both the coupling of receptors to G proteins, the function of these proteins, and their abundance in human peripheral mononuclear leukocytes stays unaltered by the aging process.