A crystal slip system model has been developed for the analysis of gas turbine single crystal Ni-base superalloys and has been implemented in finite element analysis software using the established theory of crystal plasticity. The model incorporates many of the dominant deformation mechanisms seen in these high temperature materials, which have been determined from mechanical testing and microscopic analysis. In particular slip is considered on the {111}[011] and {111}[112] slip systems, the former are denoted type I systems and the latter type II. Type I systems are dominant at high temperature in orientations close to [001], in other orientations or at lower temperatures (700-800 degreesC) type II systems become active. When the type II systems are activated they give rise to significant transient creep strains at low temperature, which can be more than 5-6% in magnitude. (C) 2003 Elsevier B.V. All rights reserved.