This thesis reports the results of an experimental investigation of the effect of buoyancy forces on turbulent upflow of air in a vertical pipe under condit.io:1s of constant wall heat flux at Reynolds numbers of 5000 to 14000. Preliminary velocity and axial turbulence intensity measurements in isothermal flows for Reynolds numbers of 5000 to 32000 are also reported. Velocity and temperature distributions were measured over a range of heat fluxes at Reynolds numbers of approximately 5000 and 8000 and at a single heat flux at a Reynolds number of 14000.