Raman spectroscopic measurements have been used to follow changes induced in the conformation of cellulose when pulps are treated with caustic solutions of different strength. The degree of conformational transformation was compared with the response of kraft and sulfite pulps in derivatization reactions. When treated with caustic solutions at the threshold of the mercerization range, conversion of the kraft pulp was much more limited than that of the sulfite pulp. This is taken as an indication of greater constraint on molecular mobility in the kraft pulp; it is speculated that cross-links, either physical or chemical in origin, are responsible for this constraint. When the kraft pulp is treated with a caustic solution that is strong enough to overcome these constraints (25%), its response becomes comparable with that of the sulfite pulp. See also AATA 181303. -- AATA