Modification of the fiber surface during processing has been studied on three wools of Aus tralian fine, domestic fine, and domestic medium grades. Samples were taken from each wool at each stage of their manufacture into a worsted fabric by the Forstmann Woolen Company. Groups of fibers, selected randomly from each sample, were treated with Pauly reagent and ex amined microscopically. The amount of color on the fiber was estimated visually, and the amount of scale disturbance was assessed. The rate of exhaustion of Anthraquinone Blue SKY was also measured on samples from each processing stage. A consistently increasing amount of surface modification was observed with all three wools as the manufacturing process advanced. The susceptibility of the wools to staining with Pauly reagent and their rate of taking up Blue SKY from a dye bath also increased. However, all of these changes were reversed by a steaming process such as is frequently used in normal worsted processing. It was concluded that the dye susceptibility of processed wool is related to the amount of scale disturbance of the fibers and that the epicuticle does not seem to constitute the only major resistance to dye penetration.