In situ SAXS experiments were performed as water-swollen lyocell (Tencel(R)) fibres were repeatedly dried at 160 degrees C and re-wet. In all cases, the void size increased and the void volume fraction decreased on drying. The water-swollen fibre apparently consists of a network of small voids between many of the elementary fibrils. As the water is driven out of the fibre, smaller voids collapse leaving dense regions and a few large voids. Consecutive drying cycles affected the pore structure. The wet Volume fraction of voids and the void length parallel to the fibre axis decreased with increasing cycle number. The void parameters perpendicular to the fibre axis did not change significantly. Pretreatment by autoclaving and drying at 160 degrees C resulted in similar changes. The observations are consistent with the homification mechanism proposed for native cellulose fibres in which the voids are partially or totally ＇zipped up＇ during drying by the formation of additional hydrogen bonds between elementary fibrils and are thus not able to reopen fully on re-wetting [Stone JE, Scallan AM. Technical section of the British Paper and Board Makers＇ Association, 1996, p. 1; Laivins GV, Scallan AM. Transcript of products of paper making. In: Baker CF, editor. Tenth Fundamental Research Symposium, vol.2. Oxford: Pira International, 1993, p. 1235; Scallan AM. Fibre-water interactions in paper making. 1. Transactions of BPBIF Symposium, Oxford, 1977]. (C) 2000 Elsevier Science Ltd. All rights reserved.