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Purpose: To specify the cues for the discrimination of orientation in depth in axis orientation selective (AOS) neurons., Methods: We analyzed the responses of AOS neurons in the monkey caudal intraparietal sulcus (cIPS) region using binocular disparity stimuli generated by stereoscopic 3 D computer graphics., Results: Most AOS neurons (20/27) were sensitive to binocular disparity and showed tuning to the orientation of a slit in the sagittal plane with orientation disparity cues. For 12 neurons we also used an array of discs or dots instead of slits to eliminate orientation disparity. Half of the neurons (6/12) responded better to the slits than to the discs or dots, suggesting that they were sensitive to orientation disparity. Five neurons (5/12) responded equally well to the discs or dots suggesting that they were more sensitive to the gradient of horizontal disparity than to the orientation disparity., Conclusion: Both orientation disparity and disparity gradient were likely to be integrated in the cIPS area to represent axis orientation of an object in space.