This paper proposes three different test programs, with varying degrees of experimental effort, for the determination of model parameters for a steel plasticity model proposed by Granlund(1997). The proposed programs are based on the experiences from the extensive biaxial testing that has been performed by the authors. The biaxial testing comprised five steel grades. Two structural, Granlund(1997), and three stainless steel grades, Olsson(1998). The biaxial testing has been performed utilizing a unique testing equipment, developed at the Division of Steel Structures, Lulea University of Technology, that allows for testing in the full principal stress plane sigma sub 1 - sigma sub 2 , i.e. also in compression. The use of the plasticity model is most advantageous in cases where stress reversals can occur, such as for instance in buckling problems, but it can also be beneficial in simpler cases including e.g. residual stresses caused by welding. The model does compared to a simple plasticity model utilizing isotropic hardening only require three additional parameters and thus it has the potential of being practically used. Materials: S275, Domex 690, 304 and 2205 steel