During flotation, hydrophobic particles detach from the bubbles in the froth phase due to bubble coalescence, bubble bursting and froth overloading. While some detached particles drain back to the pulp phase, a fraction may selectively re-attach to the bubbles rising in the froth. This should result in grade profiles through the froth. Although this process has not been studied in much detail, qualitative evidence suggests that it occurs in deep, lightly loaded froths, such as in flotation columns. A mathematical model was developed to describe the process. The model rakes account of the extent to which bubble surfaces are covered by floating particles and the changing characteristics of the froth with increasing height above the pulp-froth interface. These include the changes in the gas holdup and the bubble size. The model has been verified qualitatively by testwork in a laboratory-scale column flotation cell. Results indicated that the probability of attachment increased with an increase in the hydrophobicity of the draining particles, an increased bubble frequency and an increased gas holdup. It decreased when the coating of bubble surfaces was increased by the addition of fine floatable material. It further appears that a critical ratio of water to hydrophobic solids in the froth is required if selective attachment is to occur.