Primary and steady state creep in a Fe-3 wt% Si solid solution was investigated in the temperature interval 823-973 K at applied stresses which resulted in minimum creep rates of 10(-7)-10(-3) s(-1). The creep curves were described by the McVetty equation and the dependence of its parameters on external variables was discussed. For a constitutive description of the curves based on the choice of the internal stress as a single internal variable, a set of constitutive equations that include the experimentally found relation between the creep rate and the internal stress were suggested. Consequences resulting from this suggestion for the internal stress values which follow from the analysis of the creep curves were discussed.