Determination by X-ray techniques of stacking-fault densities in platinum was attempted. Heavily deformed platinum was annealed under varying conditions of temperature and time. The X-ray method used for measuring stacking-fault densities was found to lack accuracy for the unequivocal determination of the type of thermal activation process that leads to the loss of stacking faults during annealing. Results suggested that the process may be a first order process with an activation energy of 0.5 ± 0.3 ev. This activation energy is sufficient for extended dislocations to cross each other in platinum, with the formation of jogs. Quenched-in vacancies were found to have no detectable effect on X-ray reflections.