Recent results of Whiting and Goring on the acid-sulphite pulping of Isolated middle-lamella and secondary-wall tissues of spruce wood have permitted a aw theoretical analysis of the topo-chemistry of delignification. Unlike the previous data obtained by U.V. microscopy of thin wood sections, the new results did not require the postulation of a different reaction rate constant in each morphological region. By assuming only that the crosslink density of the secondary wall was about 0.75 of that of the middle lamella, gel degradation theory provided a good fit to the experimental points. This analysis suggests that the topochemical effect observed in acid-sulphite pulping is determined solely by lignin chemistry. The contrast in the conclusions derived from the two sets of data leads to consideration of which of the data sets is more representative of the topochemistry in the pulping of Intact wood.