Experiments on anesthetized cats with partial lesions of the spinal cord show that reticulospinal pathways in the ventral part of the lateral funiculus take part in the polysynaptic reflex inhibition caused by stimulation of ipsi- and contralateral reticular formation. The reticulofugal volley in the ventrolateral funiculus produced relatively short (up to 7 ms) inhibitory PSP in some motoneurons of the internal intercostal nerve and at the same time long-lasting depression of EPSPs evoked by high-threshold segmentary afferents. This volley also caused inhibitory PSP in segmental interneurons (in 14 out of 91, i.e. 15.5%). The IPSPs lasted no longer than 100 ms, while the segmentary excitatory responses of 21 out of 43 interneurons were depressed for 120-500 ms. The described inhibitory action of the lateral reticulospinal system on segmentary reflex pathways is suggested to be caused by several synaptic mechanisms which do not necessarily include hyperpolarization of spinal neurons. Possible mechanisms of such inhibition are discussed.