Within the framework of the Mises yield criterion generalized to hexagonal crystals proposed by the authors, the problem of determining the stress tensor depending on the strain rate tensor and the applied external pressure is solved. The cases of plane and uniaxial deformation are considered in detail for an arbitrary orientation of the crystal lattice. For the cases of plane and uniaxial deformation, diagrams of stress level lines for the onset of plastic flow are plotted. Diagrams are given for the components of the stress tensor deviator.