1. We studied the effects of anoxia on excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) evoked by electrical stimulation in the stratum radiatum in concomitantly recorded pyramidal cells and interneurons of the CA1 region of rat hippocampal slices. We used the blind whole cell patch-clamp technique, and anoxia was induced by switching perfusion of the slice from oxygenated artificial cerebral spinal fluid (ACSF) to ACSF saturated with 95% N2-5% CO2 for 4-6 min. 2. As in pyramidal neurons, anoxia induced in interneurons outward currents, during and shortly after the anoxic episode. Both currents were, however, significantly larger in interneurons than in pyramidal neurons. 3. EPSCs are more rapidly depressed by anoxia in interneurons than in simultaneously recorded pyramidal cells. 4. In pyramidal neurons, polysynaptic IPSCs (pIPSCs) evoked by conventional distant stimulation (> 1 mm) are more sensitive to anoxia then EPSCs. In contrast, in interneurons, anoxia blocks with a similar latency EPSCs and polysynaptic IPSCs. 5. To determine whether this block of pIPSCs in pyramidal cells is due to a shift in driving force or a change in conductance, we examined the current (I/V) relationships. The block by anoxia of pIPSCs is due to a reduction of IPSC conductance (> 98%) that occlude other events including the shift of IPSCs reversal potential (ECl).(ABSTRACT TRUNCATED AT 250 WORDS)