A plain bearing for guiding a rail comprises a bearing housing (4) displaying a single, cylindrical through-opening (5), and a sliding element (6), which is supported in the through-opening (5) and which forms a sliding opening (7), in which the rail (2), by means of a rail head (9), is mounted in displaceable fashion, where the through-opening (5) and the sliding opening (7) are laterally open towards the outside at an angle .mu. formed by an engaging opening (10), through which the rail head (9) of the rail (2) can engage the sliding opening (7). To reduce wear and permit a low design height, the sliding opening (7) displays a polygonal cross-section, where at least one of the interior side surfaces (11) of the sliding element (6) that delimit the sliding opening (7) is essentially perpendicular to the greatest force expected during operation and transmitted via the sliding element (6) to the rail head (9).