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Dislocation mobility studies indicate that the symmetrical form of the energy barrier and the corresponding sinh expression, usually assumed in the analysis of strain relaxation, cannot be reconciled with the results obtained in dislocation velocity measurements. In the present study an expression for strain relaxation is derived from the transition state theory for the asymmetrical forms of the energy barrier. The expression obtained is in full agreement with the dislocation velocity measurements. Three typical energy barrier shapes are analyzed in detail. One of the barriers is identified to be associated with logarithmic strain relaxation often observed during the initial, high stress period. For two of the barriers considered, the strain is shown to approach asymptotically to a limiting value. The analysis indicates that internal stress cannot be relieved completely when the energy barrier is asymmetrical.