Anisotropy in flow behavior of cold worked and stress-relieved Zr-2.5wt%Nb pressure tube alloy was characterized by performing tensile tests in the temperature range of 298-823 K and under a constant nominal strain-rate of ∼3 × 10-4 s-1. Results showed that both yield and ultimate tensile strengths of this alloy decreased gradually with increasing test temperatures, with a rapid fall in strengths above a temperature of 623 K. The tensile ductility did not change appreciably up to 673 K but increased rapidly above this temperature. A strain energy model was developed to explain the occurrence of dynamic strain ageing (DSA). Analysis of the true stress-strain behavior suggested that the flow hardening or softening behavior of this alloy can be expressed in the form of a constitutive relationship comprising of a constant, work-hardening term and a term representing flow softening due to recovery. © 2005 Elsevier B.V. All rights reserved.