It is shown that the ratio of the resistivity increments injected by irradiation at low temperature into deformed and into annealed specimens is related to the difference in fractional recovery that occurs in Stage I between the two specimens. Using this relation the ratio of resistivity increments to the resistivity increment due to dislocations is computed for a number of different irradiations. For a given metal and type of irradiation the enhancement of resistivity increment in a deformed specimen is closely proportional to its dislocation resistivity. It is shown that this is more in accord with explanations of the enhancement based on greater defect production per unit irradiation dose than with explanations based on greater specific resistivity of Frenkel pairs in the presence of large defect concentrations.