Receptive-field properties of 273 relay (principal, P-) cells of the dorsal lateral geniculate nucleus (LGd) were studied in urethane-anesthetized albino rats, to see if there is some relation between the visual property and the conduction velocity of afferent optic nerve fibers. According to properties of the receptive-field center, P-cells were classified into 2 types, common (89%) and uncommon (12%). The common type consists of OFF-phasic, ON-phasic, ON-tonic and ON-OFF-phasic cells, while the uncommon type includes ON-inhibited, moving-sensitive, ON-OFF-inhibited, simple-cell-like and complex-cell-like cells. The mean response latency to single optic chiasm shocks increases in the order of OFF-phasic (1.94 ms), ON-phasic (2.35 ms), ON-tonic (2.87 ms), ON-OFF-phasic cells (3.04 ms) and uncommon type (3.18 ms). The mean size of the receptive-field center in each of the 4 common types was smaller than that in the uncommon type; 6-7.degree. vs. 11.degree.. From responsiveness to moving light spots with speeds > 25-30.degree./s, P-cells of the common type were divided into the fast- and slow-movement-sensitive cells. The ratio of occurrences of fast- to slow-movement-sensitive cells decreases in the order of the OFF-phasic (2.7), ON-phasic (2.4), ON-tonic (1.1) and ON-OFF-phasic types (0.06). The optic chiasm latencies were < 2.5 ms in most of the fast-movement-sensitive cells while the reverse was true for most of the slow-movement-sensitive cells. The rat LGd mainly consists of Y- and W-like P-cells and that the Y/Wt type dichotomy of P-cells approximately corresponds to the previously established fast/slow classification.