As a consequence of previous work on interthalamic relationships, the possibility has been evaluated that the thalamic relay for the somatosensory pathways ascending from one side of the body (nucleus ventralis posterolateralis, VPL) may be subjected to some inhibitory control whenever the contralateral corresponding relay nucleus is activated. Electrophysiological experiments were performed in locally anaesthetized, curarized cats, previously submitted to proper cortical ablations and/or to callosal transection in order to disrupt possible thalamo-cortico-thalamic circuits. Relayed activity in the side chosen for recording was elicited by direct electrical stimulation of one of the following structures: i) ipsilateral decussated lemniscal bundle; ii) contralateral bulbar relay-nuclei; iii) contralateral spino-cervico-thalamic path, at the C₃-C₄ level. The relaying ability of the VPL nucleus was evaluated by recording the evoked potentials from the ipsilateral subcortical white matter (mass responses; killed-end recording) before, during, and after the stimulation of the contralateral VPL. According to the evidence obtained, the transfer of the ascending messages through the VPL nucleus is strongly reduced after conditioning "transversal" volleys produced by direct stimulation of the contralateral VPL and ineffective in eliciting per se apparent excitatory reactions.