To study the functional projection patterns of the primary afferents in the spinal cord, the postsynaptic responses of substantia gelatinosa (SG) neurones evoked by L5 dorsal root stimulation (DRS) were examined from the neurones located at L2 to S1 in horizontal slices of the adult rat spinal cord using a blind whole-cell patch-clamp technique. In the voltage-clamp mode, the L5 DRS evoked the A- and C-afferent-mediated excitatory postsynaptic currents (EPSCs) in more than 70% of the neurones tested at the L5 level. Both A- and C-afferent EPSCs were also recorded in more than 50% of the neurones at L4. At L3 and L6, the number of neurones receiving the C-afferent EPSCs (>40%) was significantly greater than that of A-afferent EPSCs (<20%). On the other hand, the A- and C-afferent-mediated inhibitory postsynaptic currents (IPSCs) elicited by the L5 DRS were almost equally observed from L2 to S1. In the current-clamp mode, the L5 DRS evoked the A- and C-afferent-mediated excitatory postsynaptic potentials (EPSPs), some of which initiated the action potentials (APs). Most of the A-afferent-mediated APs were limited at the L5 level, while the C-afferent-mediated APs were observed at L5 and L4. Since the L2 DRS-evoked APs in the L2 SG neurones were suppressed by the L5 DRS, the wide spread distribution of the inhibitory inputs was considered to be functional. These findings suggest that the excitatory projection of the C afferents to the SG neurones was thus spread more rostrocaudally than that of the A afferents, thereby contributing to more diffuse pain transmission. In addition, the wide-spread distribution of the inhibitory inputs may thus play a role as a lateral inhibitory network and thereby prevent the expansion of the excitatory inputs of noxious stimuli.