Abstract: An operating method and a rolling mill train for continually rolling a profiled billet to a predetermined finished cross-sectional shape of accurate dimensions by means of successively arranged rolling mill stands with pairs of rolls, wherein the axes of the pairs of rolls extend perpendicularly to each other. The pairs of rolls have oppositely located pass screws which determine the cross-sectional shape of the rolled steel section billet which travels through the pairs of rolls. The billet is sized in one or more roughing stands locally in a circumferential portion of the cross-section thereof which, after leaving the last roughing stand, runs in the subsequent main stand into the region of a contact line of the two rolls of the main stand, such that the entire material of the billet running into the main stand completely fills out the pass of the main stand without significantly deforming the region of the contact line of the two rolls of the main stand.