Abstract The phenomenological constitutive equation given below, for uniaxial steady state creep, i.e. ϵ= K 1 Oe −ϵO⧸kT sinh K 2(σ−σ O) log 16ϵ O kT −K 2(σ−σ O) has been derived from first principles and applied to AISI316 stainless steel, pure polycrystalline aluminum and copper. A single micromechanism has been found sufficient to predict the data throughout the entire test temperature and stress range. The equation above has an intrinsically atomic basis as it has been obtained through the notion of intermal variables in the context of the absolute reaction theory of Eyring. The physical meaning of the internal variables and the foundation of their associated evolution equations are established clearly in terms of averages of atomic motions over the energy barriers, under application of an external stress field. It is this concept that gives one hope that a sound thermodynamic and physical foundation of irreversible thermodynamics with internal variables has been found from microscopic considerations.