Recent tests of a 250 m(2) m(-3) structured packing in a 1.22 m diameter column have produced some unanticipated results. Using two quite different systems, mass transfer performance in a relatively short 1.69 m bed was significantly better than previous results in a longer 3.78 m bed. No bed length effect was found on pressure drop. Two different severe vapour maldistributions were studied using a vacuum system with the 1.69 m bed. No significant effect of vapour maldistribution on mass transfer efficiency, capacity and pressure drop was observed. The HETP 'hump', or deterioration of mass transfer performance, previously reported in a 3.78 m bed, was again found in the short bed using 11.4 bar butane. However, tests with a 133 m(2) m(-3) packing did not show the hump in a 3.81 m bed. The experimental results are compared with predictions from various literature models.