Rates of decrease in crystallinity, as measured by x-ray crystallinity index, have been followed throughout periodate oxidations of cotton cellulose and formaldehyde-treated cotton celluloses. Depending upon the conditions under which the agent was introduced, a low level of formaldehyde crosslinks exerted small or large retardation on the rate of decrease of crystallinity index. The extents of decrystallization per unit of oxidation of cotton and crosslinked cotton celluloses are substantially smaller in the initial phase of oxidation than in the later stage, indicative of preferential oxidative attack in the early stage on chain segments of predominantly noncrystalline regions. Relative to unmodified cotton, crosslinked cotton celluloses are characterized by more extensive decrystallization per unit of oxidation in the early phase of oxidative attack (to approx. 40%). From these data, supplemented by electron micrographs and solubilities in cupriethylenediamine hydroxide, uniformity of distribution of crosslinks is shown to increase in this series of formaldehyde-modified cotton celluloses (at the same level of agent) in the order: form D cotton (nonaqueous treatment) < form W cotton (aqueous treatment) < form V cotton (vapor treatment). Effectiveness of crosslinking (i. e., composite of number of linkages, ratio of intermolecular to intramolecular bonds, low degree of polymerization in crosslink) is indicated to increase from form W to form D to form V cotton.