This paper concerns polymeric composite columns manufactured by the pultrusion process. The behaviour of such members is investigated to provide a basis for future assessment of design methods. The minor-axis buckling characteristics of twelve wide-flange columns are presented. The main parameters varied are height (6·3 m, 4·8 m and 3·3 m) and nominal cross-sectional dimensions (152 × 152 × 9·53 mm, 203 × 203 × 9·53 mm and 203 × 203 × 12·7 mm). Deformation and failure characteristics are presented. It is found that theoretical Euler critical buckling loads generally correlate well with maximum test loads and critical loads derived from Southwell plots. A detailed discussion is presented to show that differences are due to imperfections in the column specimens and the test rig. At the shortest column height, the onset of local compression flange buckling is found to lower resistance by way of modal-coupling with the global bending deformation.