The effects of enzymatic removal of xylan and glucomannan from pine and birch kraft pulps on the pore size distribution and median pore width of the pulp fibres were determined by modified solute exclusion and NMR techniques. With the NMR method, clearly higher median pore sizes of the kraft fibres were obtained compared with the solute exclusion method. However, the effects of enzymatic treatments on pore size distributions and median pore widths of fibres were detected by both techniques. An increase in the pore width of both pine and birch kraft fibres was observed even after a limited xylanase treatment. The NMR technique appeared to be more suitable than the solute exclusion method for determination of the further increase of the median pore width and the widening of the pore size distribution of fibres by a more extensive xylanase treatment. Both techniques revealed an increase of the median pore width of fibres caused by the extensive removal of pine kraft pulp glucomannan. Despite their basic differences and specific limitations, both the NMR and solute exclusion techniques showed the enzymatic effects on the porosity of pulp fibres.