Abstract: A process of automatic yarn spinning-in in the spinning unit of an open-end rotor spinning machine of an automatic service device provided with a control unit having a programmable microprocessor control system for controlling the spinning-in cycle and the automatic adjustment of spinning-in parameters modified according to successive verifying tests which are performed by the automatic service device which is either arranged in the individual spinning units, or as a unit traveling along the machine. By successive tests, spinning-in parameters are adjusted for an interval for yarn return to the spinning rotor as well as for determining the start of fiber feeding. The spinning-in parameters can be corrected by further verifying tests in spinning units with various dynamic characteristics.