1. Bipolar cells were enzymatically (papain) dissociated from the mouse retina. Responses to exogenously applied glycine and GABA were recorded using the whole-cell voltage clamp method (pipette solution contained 121 mM-Cl-). Both glycine and GABA evoked inward currents in cells voltage clamped at negative membrane voltages (e.g. -60 mV) and superfused with the control solution containing 146 mM-Cl-. 2. Polarities of both glycine- and GABA-induced currents reversed near 0 mV under our control conditions. The reversal potential depended on both external [( Cl-]o) and internal (intrapipette; [Cl-]p) Cl- concentrations, but on neither Na+ nor K+ concentration. The reversal potentials were very close to the calculated equilibrium potential for Cl- estimated by using the Nernst equation with various external and internal Cl- activities. 3. The sensitivity to both glycine and GABA was highest at the axon terminal bulb. 4. Glycine-induced responses were antagonized by 10 nM-strychnine (competitively and non-competitively), but by neither bicuculline nor picrotoxin. GABA-induced responses were antagonized by 30 microM-bicuculline (competitively) and 30 microM-picrotoxin (non-competitively), but not by 100 nM-strychnine. Muscimol was as effective as GABA. Baclofen evoked no response even at 100 microM and did not modulate voltage-dependent Ca2+ current. Pentobarbitone (10 microM) increased the sensitivity to GABA. These observations suggest that glycine and GABA worked on separate receptor molecules and that the receptors for GABA were GABAA type. 5. The present study suggests that glycine and GABA, both putative neurotransmitters of amacrine cells, mediate inhibition of bipolar cells in the mouse retina.