In the lower zone of the iron making blast furnace, liquid iron and slag descend counter-current to reducing gases through a packed bed of coke. The characteristics of the flow of these liquids and their holdup influence product quality and furnace operation. The present study aimed to establish the criteria for the passage of slag through the narrow pore necks that form between coke particles. The flow of slag through coke pore necks has been simulated using an experimental technique that assesses slag flow from a funnel entering a narrow channel of known diameter. Synthetic coke was mainly used to minimise experimental uncertainty associated with the use of variable industrial coke and to allow control of the coke mineralogy. Industrial coke and graphite were also tested. Pellets of slag with compositions in the CaO-Si02-MgO-Ab03 system were melted in the coke funnels and heated to 1 500°C under argon, then held at temperature for a certain time. After cooling, the passage of slag through the channel was determined and the interactions of the slag and coke were characterized. Variables assessed included slag composition, coke mineralogy and channel diameter. For the slags and cokes studied, the minimum channel diameter that allowed slag to flow was between 4.4 and 5.0 mm. For smaller diameters, slag did not flow through the channel. The flow mechanism was discussed in terms of a simple gravity and capillary/interfacial force analysis of the system.