GABA (γ-aminobutyric acid), the main inhibitory neurotransmitter in the central nervous system is also present in the pancreatic islet β cells where it may function as a paracrine molecule and perhaps as an immunomodulator of lymphocytes infiltrating the pancreatic islet. We examined CD4 + and CD8 + T cells from diabetes prone (DR lyp/lyp ) or resistant (DR +/+ ) congenic biobreeding (BB) rats for expression of GABA A channels. Our results show that BB rat CD4 + and CD8 + T cells express α1, α2, α3, α4, α6, β3, γ1, δ, ρ1 and ρ2 GABA A channel subunits. In CD8 + T cells from DR lyp/lyp animals the subunits were significantly upregulated relative to expression levels in the CD8 + T cells from DR +/+ rats as well as from CD4 + T cells from both DR lyp/lyp and DR +/+ rats. Functional channels were formed in the T cells and physiological concentrations of GABA (100nM) decreased T cell proliferation. Our results are consistent with the hypothesis that GABA in the islets of Langerhans may diminish inflammation by inhibition of activated T lymphocytes.