The orientation sensitivity of LGN cells to flickering square-wave gratings was measured in urethane-anaesthetized paralyzed cats. The mean ratio of the amplitude of peak responses to optimally oriented gratings to that elicited by gratings of the least effective orientation was 3.0 +/- 0.3 (S.E.). 58% of the recorded neurons responded best to orientations within 30 degrees of the meridional line joining their receptive field center with the fixation points (area centralis), implying that they were more sensitive to visual contours pointing to the center of the retina.