Using guinea-pig isolated whole brain preparation in vitro, synaptic responses to electrical stimulation of auditory nerves were examined in intracellularly recorded and stained neurons of posteroventral and dorsal divisions of the cochlear nucleus. Stimulation of the contralateral auditory nerve evoked exclusively IPSPs in 70% of neurons, with amplitude of 2.3+/-1.2mV. Neurons of all major cell types were inhibited from the contralateral side. In the majority of responding cells (78%) IPSPs were induced at latencies of 3-9 ms suggesting di- and trisynaptic connections from contralateral auditory afferents or, respectively, mono- and disynaptic connections from the contralateral cochlear nucleus. Few cells responded with long-latency IPSPs (13.5-23ms), indicating involvement of polysynaptic pathways. These data demonstrate the existence of functional, direct and indirect inhibitory connections between the cochlear nuclei.