1. SB-205384, and its (+) enantiomer (+)-SB-205384 were tested for their modulatory effects on human GABA(A) receptor subunit combinations expressed in Xenopus oocytes by electrophysiological methods. 2. The slowing of the decay rate induced by SB-205384 on native GABA-activated currents in rat neurones was also seen on GABA(A) currents in oocytes expressing human GABA(A) subunits. This temporal effect was observed for the alpha3beta2gamma2 subunit combination with little effect in subunit combinations containing either alpha1 or alpha2. 3. Potentiation of the peak amplitude of the GABA-activated currents by SB-205384 or (+)-SB-205384 was less specific for a particular subunit combination, although the greatest effect at 10 microM drug was seen on the alpha3beta2gamma2 subunit combination. 4. In contrast, zolpidem, a benzodiazepine site modulator, did not significantly slow decay rates of GABA(A) currents in oocytes expressing the alpha3beta2gamma2 subunit combination. Zolpidem, as expected, did selectively potentiate GABA-activated currents on oocytes expressing the gamma2 subunit compared to those containing the gamma1. 5. The results show that the novel kinetic modulatory profile of SB-205384 is selective for the alpha3beta2gamma2 subunit combination. This suggests that the compound is binding to a novel regulatory site on the subunit complex.