Cytoplasmic injection of Xenopus oocytes with cDNA-derived RNA (cRNA) encoding a wild-type Drosophila melanogaster GABA receptor subunit (Rdl) resulted in functional expression of a GABA receptor homo-oligomer. Membrane currents recorded in response to muscimol, trans (TACA)- and cis (CACA)-4-aminocrotonic acid reversed at membrane potentials close to ECl- and were insensitive to 1.0 x 10(-4) M bicuculline methiodide. An order of potency of GABA approximately muscimol approximately TACA > CACA > glycine was observed. Response of the expressed Drosophila Rdl receptor to GABA was reduced by t-butylbicyclophosphorothionate (TBPS), 4-n-propyl-4'-ethynylbicycloorthobenzoate (EBOB), picrotoxinin and the novel insecticide, fipronil (all at 1.0 x 10(-5) M).