Experimental measurements were made in a rotating-cavity rig with an axial throughflow of cooling air at the centre of the cavity, simulating the conditions that occur between corotating compressor discs of a gas-turbine engine. One of the discs in the rig was heated, and the other rotating surfaces were quasi-adiabatic; the temperature difference, between the heated disc and the cooling air was between 40 and 100 °C. Tests were conducted for axial Reynolds numbers, Rez, of the cooling air between 1.4 × 103 and 5 × 104, and for rotational Reynolds numbers, Reφ, between 4 × 105 and 3.2 × 106. Velocity measurements inside the rotating cavity were made using LDA, and temperatures and heat flux measurements on the heated disc were made using thermocouples and fluxmeters. The velocity measurements were consistent with a 3D, unsteady, buoyancy-induced flow in which there was a multicell structure comprising one, two or three pairs of cyclonic and anti-cyclonic vortices. The core of fluid between the boundary layers on the discs rotated at a slower speed than the discs, as found by other experimenters. At the smaller values of Rez, the radial distribution and magnitude of the local Nusselt numbers, Nu, were consistent with buoyancy-induced flow. At the larger values of Rez, the distribution of Nu changed, and its magnitude increased, suggesting the dominance of the axial throughflow.