A theoretical analysis is made of the influence of a hydrostatic pressure on dislocations. It is shown that such an analysis must be made using the nonlinear theory of elasticity. The predicted enhancement of the interaction between dislocations in a hydrostatically compressed crystal is used in a discussion of the influence of pressure on the nature of the strain-hardening curves of fcc crystals. This discussion is based on well-known models. The predicted increase of the strain hardening during the initial deformation stages is in agreement with the published experimental data.