In the froth flotation of ultra-fine particles, the recovery and purity of the final product obtained depend largely on the froth structure, which in turn is affected by reagent adsorption on the solids. In this study, ultra-fine particles (5 mu m size fractions) of two low rank British coals were used in the flotation tests. The tests were carried out using only one of two different non-ionic reagents; diacetone alcohol and 2-ethyl hexanol. The froth structure can be changed significantly by addition of reagent. It was observed that when the froth structure changes from a spherical to a polyhedral structure that the flotation performance changes significantly. Previous measurements of the internal pore distributions showed marked differences between the Rawdon and Bickershaw coals. Also the flotation performance of each coal differed significantly according to the reagent used. It is postulated that the differing behaviour of the coals can be attributed to the fractional amount of the total reagent adsorbed on the interior pore surfaces.