This article demonstrates an asymmetry between line orientations in the flanker task. The first two experiments show that when the target is either a vertical or a horizontal line, diagonal line flankers tilted either to the right or to the left have the same effect as incongruent flankers. When the target is a diagonal line tilted either to the right or to the left, vertical or horizontal line flankers do not have the same effect as incongruent flankers. Experiments 3 and 4 demonstrate that this asymmetry is not caused by dynamic aspects of the processing. Together these experiments suggest that diagonal iines outside the central focus of attention appear to be similar to both vertical and horizontal lines. Experiment 5 shows that despite this similarity, visual search for a vertical or a horizontal line target among diagonal line distractors is not affected by the number of distractors. A hypothesis concerning the nature of the representations of line orientations outside the central focus of attention is suggested. Other implications of this study are briefly discussed. 9