The difference in the stress for plastic deformation between the mixed state and the superconducting state has been measured in a series of lead‐indium crystals. These measurements show that the change in drag stress between the two states varies in the same manner as does the ultrasonic attenuation in a type‐II superconductor. Quantitative agreement between the present results and Maki’s theory of transport properties in dirty superconductors is found for higher solute concentration crystals. These results show that dislocation motion in these lead‐indium alloys can be treated as an underdamped oscillator.