The effect of liquid maldistribution on the separation performance of structured packing was studied using an adjustable liquid distributor. The tests were conducted ina 1.2m diameter column using a 3.78m bed of Sulzer Mellapak 250. Y with the cyclohexane/n-heptane system at atmospheric pressure. Results indicate that structured packing is less sensitive to under-irrigation of the wall zone than random packing. On the other hand, structured packing appears to be more sensitive to random maldistribution than random packing. There is almost no loss in efficiency when the pour point density is reduced from 103 pp/m(2) to 26 pp/m(2).