A localized lesion was made in the nucleus reticularis pontis caudalis (NRPC) and the nucleus reticularis gigantocellularis (NRG) by kainic acid injection, and its effects on visually triggered orienting eye and head movements in the horizontal direction were investigated in alert head-free cats. Before the lesion, trained cats could orient the head and eyes to the target presented in the periphery of the visual field, with rapid eye (saccade) and swift head movements. After the unilateral lesion, they were unable to direct the head toward the target on the lesioned side in 64% of the trials tested during 2 weeks after the lesion, while they managed in 36% of the trials, although the movement was reduced both in speed and amplitude. The saccadic eye movement was completely absent through all trials. In contrast, eye and head movements to the intact side were as normal as the control. The present results suggest that the NRPC and NRG play an essential role in relaying a descending command of ipsiversive visually triggered orienting movements of eyes and head in the horizontal direction.