The accessibilities of the hydroxyl groups of the D-glucopyranosyl units of slack mercerized grey yarn and of the same yarn restretched to its original length are compared with those of the original grey yarn, a purified printcloth, and a hydrocellulose. The study involved reactions of the celluloses with N,N-diethylaziridinium chloride under conditions which ensure minimum conversion of the reagent by hydrolysis to 2-hydroxyethyldiethylamine. Amylose was taken as a reference material in which the hydroxyl groups are assumed to be completely accessible. Selective accessibilities of the hydroxyl groups at C-6 and C-3 relative to those at C-2 were determined with the same reagent by a method whose development has been described earlier. The results of this study are expressed as fractions of the hydroxyl groups at C-2, C-3, and C-6 that are accessible to the reagent.