Abstract: The invention relates to a method of friction stir welding in which use is made of a rotating friction stir welding tool, said tool having a probe, the method comprises, (a) temperature control of the tool during welding of a workpiece of hard to weld materials by passing a temperature controlling coolant through one or more channels in the tool in order to control the temperature of the probe, thereby removing excessive heat from the tool and from the area of the workpiece being welded, (b) said coolant having a predetermined first temperature upon entering the tool, (c) measuring a second predetermined temperature indicative of the tool probe temperature, and (d) controlling the welding process such that the tool probe is kept essentially at a predetermined tool probe temperature. The invention also relates to a combination for performing the method.