Dislocation motion in crystals is usually measured on loops generated from a deliberately introduced nucleating center such as a scratch. In germanium crystals it has been noticed that motion of an individual loop is usually asymmetric as observed by etch‐pit techniques. The asymmetry has been assumed to arise from motion of dislocations having different character. The validity of this assumption was tested directly by x‐ray topographic contrast experiments on crystals of germanium and silicon. From appropriate reflections that give either a strong or vanishing contrast it is possible to determine the Burgers vector of the dislocation loop. For both bending and compression tests, dislocation loops generated from a scratch and subsequently moved have a Burgers vector in the maximum resolved shear stress direction. Thus, for the specimen orientation ⟨123⟩ commonly used in velocity experiments both ends of the dislocation loops intersecting the surface of observation have the same character. In some cases the asymmetry may be due to the shape of the loop. The x‐ray evidence refutes the conclusions reached by previous workers that asymmetrical motion is due to dislocations of different character.