Abstract: A method and a device for adaptive control of the weld parameters in automatic arc welding processes to weld together two workpieces. The arc is arranged to oscillate in the transverse direction of the groove and by measuring the welding current and/or welding voltage on two separate occasions during the deposition of the root run characteristic values are obtained. The values obtained on these two occasions are combined mathematically with a calculated rated value. This rated value corresponds to the height of the root bead of the weld. The discrepancy of the obtained values from the calculated rated value is used to control means arranged to set the weld parameters, thus ensuring that a homogeneous weld is obtained, irrespective of groove variations, such as variations in the gap width between the two workpieces, or variations of other factors affecting the weld.