This paper begins with a brief description of some work which provided the initial stimulus for the longstanding programme of research on buoyancy-influenced turbulent flow and heat transfer in vertical passages reviewed here. An outline is then given of the various reported studies of turbulent mixed convection in circular tubes. Theoretical considerations leading to a semi-empirical model are presented next and followed by some experimental results which validate it. The extent to which experimental data for tubes carries over to passages of other geometry is illustrated by reference to some mixed convection of heat transfer experiments with passages of annular cross section. Then, a recent study in which profiles of velocity and turbulence were measured in such a passage is reviewed. Finally a study using a plane passage heated on one surface only is also reviewed.