The article describes investigations into the topochemical reaction of alkaline bleaching of wool with hydrogen peroxide using electrokinetic measurements and electron microscopy, in order to establish tests for fiber modification or damage prior to industrial textile processing or finishing. Merino wool was bleached and cuticle prepared for examination along with the fibers. Cysteic acid content was determined using acid hydrolysis and amino acid analysis (duplicate analyses from three treatment series). The streaming-current method was used to determine zeta-potential. Fiber bundles were stained with OsO₄ and embedded in Spurr resin for examination of morphology using electron microscopy (EM). When wool fibers are oxidized with hydrogen peroxide, the extent of oxidation (as measured by the increased content of cysteic acid) correlates initially with the increase in negative zeta-potential. This levels off after about 150 minutes, indicating that all the cystine in the outer layer has been oxidized, even though oxidation continues in the remainder of the fiber. EM further reveals that the major observable oxidative attack occurs in the sulfur-rich alpha-layer of the cuticle. In addition, prolonged oxidation results in damage as well as modification to the cell-membrane complex.