For the region near thę casing in the final stage of large L. P. turbines it is particularly difficult to specify these data. The shape of the casing is complicated by bled-steam extraction belts and the highly flared wall is interrupted by axial sections at the moving blade tips to allow for differential expansion. Also a complex flow structure is produced by the interaction between the tip leakage flow from the penultimate stage and the secondary flows in the fixed blade row. To provide the information necessary for improved theoretical modelling of the flow in this region, detailed measurements have been made in L.P. turbine cylinders.