Capillary adhesion forces resulting from humidity (95%) of surrounding air at 18-20 degrees C were measured for soybean, rapeseed, white mustard and wheat grains. As opposed to other com. powders, the adhesion forces of agromaterials appeared first after a long (many hs.) humidification time. The max. value of the adhesion forces appeared repeatedly during the expts. Chem. and biol. changes inside the grains and on the grain surface due to water vapor absorption were supposed.