Horizontal optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN) (stimulus speed 0–200°/sec with 1°/sec2 constant angular acceleration) were examined before and after utriculo-sacculectomy (bilateral, two-stage) in squirrel monkeys. OKN exhibited a slight decline only after bilateral otolith end organ ablations. OKAN showed a minimal decline after unilateral operation but no change after bilateral operations. Severe OKN reduction and disappearance of OKAN after bilateral labyrinthectomy in primates should basically reflect the elimination of inputs from the cristae ampullares, and not from the macu