Protrusions at migrating high-angle grain boundaries were observed following partial recrystallization of high-purity body-centred cubic refractory metals. Their morphology is similar to that previously observed in aluminium and is in good agreement with the predictions of a kinetic model based on the sinusoidal variation of the local driving pressure along the boundary. The heterogeneous dislocation structure intersecting the boundary is considered to cause this sinusoidal variation and, therefore, the growth of protrusions in the high-purity metals.