The invention relates to a method and apparatus for fibrillating synthetic ribbons in an extrusion process for the production of, for example, grass fibers. The extrusion process creates a sheet of ribbons from an extruded foil or a multiplicity of extruded monofils, and stretches them conjointly. The ribbons are led side by side in a parallel arrangement along the circumference of a fibrillating roll with a partial wrap. To produce a pattern of fibrillation irrespective of the thickness of the ribbons and the elasticity of the ribbons, the invention provides that a multiplicity of short partial cuts is made in the ribbons by a plurality of successively engaging rows of blades on the fibrillating roll each having a multiplicity of projecting cutting tips.