The heat transfer and fluid flow characteristics of a cylindrical enclosure having both rotating and stationary walls have been investigated in the presence of coolant throughflow. The research was motivated by cooling applications in cavities and enclosures which may be situated adjacent to the rotating shaft in gas turbines, compressors, and similar devices. The test section walls consisted of a heated rotating disk, a heated stationary cylindrical shroud, and an insulated stationary disk. The coolant passing through the enclosure was air. The experiments were performed over a range of disk rotational speeds, coolant flow rates and spacings between the disks. The local heat transfer coefficients on the rotating disk were found to increase with increasing rotational speed, increasing coolant flow rate, and decreasing spacing. The shapes of the radial distributions of the transfer coefficients suggested the existence of laminar, transition, and turbulent regimes. In the laminar regime, the transfer coefficients were relatively insensitive to the coolant flow rate. For the shroud, the trends with rotational speed, coolant flow, and spacing were generally similar to those for the rotating disk. However, owing to backflows along the shroud at the lower rotational speeds, the trends were more complex in that range. Flow visualization, accomplished by smoke injection, revealed a succession of flow patterns which could be ordered according to the ratio of the coolant flow rate to the disk rotational speed.