Changes in cellulose fibril aggregation during kraft pulping and drying of kraft pulps were studied by cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance in combination with spectral fitting. An increase in lateral fibril aggregate dimensions was observed in the initial phase of delignification of the pulping. The increase in aggregate dimensions is attributed to an increased contact between cellulose fibril surfaces as a result of the removal of hemicellulose and lignin. Drying of the pulps results in even larger cellulose fibril aggregates. This process is also shown to be related to the hemicellulose content. (C) 2001 Elsevier Science Ltd. All rights reserved.