We describe a new interface-type chamber for electrophysiological studies in mammalian brain slices. Thermoregulation of the inner recording chamber is achieved using the Peltier effect and a feedback control unit. Between 15 and 40 degrees C, and for perfusion rates from 1 to 5 ml/min, the temperature can be maintained within +/- 0.1 degrees C of the command value; it can also be rapidly and reliably changed. An external bath, heated by a coiled resistor, generates a humidified, oxygenated atmosphere diffusing above the slices. Survival of neuronal tissue is excellent and stable intracellular recordings can be obtained using either sharp or patch-clamp micropipettes. Perfusion solutions can be readily exchanged, rendering this chamber suitable for the study of bath-applied neuroactive compounds.