To predict the capillary transport of free liquid during the drying of softwood, it is essential to have knowledge of capillary pressure as a function of moisture content. The dependence of the capillary pressure on the wood's moisture content is predicted with a mechanistic model and measured for isothermal moisture movement in the tangetial direction. The experimental measurements confirm the model which is formulated on the postulate that the menisci that form between the liquid and gas in the tracheid lumens control the magnitude of the capillary pressure. Lumen size variation within an annual growh ring was found to significantly affect the local capillary pressure and indicated that separate flow paths are likely to exist in earlywood and latewood.