The effects of mass injection or removal at the surface of a rotating disk on heat transfer and on the flow field about the disk are studied. Consideration is given to gaseous systems which are composed of either one or two component gases. Solutions of the equations which govern the hydrodynamics, energy transfer, and mass diffusion have been obtained over the entire range from large suction velocities to large blowing velocities. Results are given for the velocity, temperature, and mass-fraction distributions, as well as for the heat-transfer, mass-transfer, and torque requirements. The effects of the mass transfer are discussed in detail. It is shown that fluid injection sharply decreases the heat transfer at the surface.