Extracellular single neurone recordings were made in the ventrobasal thalamus of urethane-anaesthetized rats. 2. Iontophoretically and intravenously administered ketamine and MK-801 were found to be selective antagonists of responses of neurones to iontophoretically applied N-methylaspartate. 3. Both antagonists, administered in N-methylaspartate-selective quantities, reduced the synaptic responses of ventrobasal thalamus neurones to a two-second air jet directed at the peripheral receptive field.