In humans and monkeys, the intraparietal sulcus separates the superior parietal lobule from the inferior parietal lobule (IPL). Whereas in humans Brodmann's area 7 is above this sulcus, in monkeys it is below and therefore part of the IPL. In humans, the IPL consists of Brodmann's areas 39 and 40. Some investigators contend that the monkey homologue of the human IPL (areas 39 and 40) is the monkey's IPL (area 7). Others contend that it is, at least in part, in the monkey's superior temporal sulcus (STS). In humans, IPL lesions induce neglect. Although IPL lesions in monkeys also have been reported to induce neglect, the STS was involved in these lesions. We sought to learn which of these two areas, when ablated, produces neglect. Study of five adult stump-tailed macaque monkeys by making five isolated STS and six IPL lesions. Inferior parietal lobule lesions were associated with misreaching but not with unilateral neglect. Neglect was observed in association with five of the six STS lesions. With regard to neglect, STS may be the monkey homologue of the human IPL. Animals with STS lesions and humans with IPL lesions may manifest unilateral neglect because these areas are necessary for normal awareness of external stimuli. This awareness may result from the integration of the areas important in stimulus localization (the “where is it?” system) and stimulus identification (the “what is it?” system), as well as the areas important in defining the biologic importance of stimuli, such as the frontal lobes and limbic areas. © 1994 Arch Neurol All rights reserved.