Abstract: The invention is in a process for dyeing and printing fibrous materials containing hydroxy groups, in particular materials such as cotton, linen, hemp, regenerated cellulose and mixtures of these fibers together with polyester or polyamide fibers. The invention is based on the discovery that water-soluble organic dyestuffs containing at least one phosphonic acid mono-fluoride group corresponding in the acid form to the formula ##STR1## and containing at least one ionic water-solubilizing group, can be fixed reactively to the fibrous material containing hydroxy groups under alkaline conditions.The dyeings and prints obtained by the process of the invention have a very even shade and are obtained in high intensity and color depth. They are fast to light and alkali and are distinguished by a very high fastness to washing, even in the alkaline range and at elevated temperatures.