The objective of this paper is to ascertain the conditions for equivalence between chemical or osmotic loading and mechanical loading on articular cartilage. Constitutive equations for a charged-hydrated-soft tissue are given and chemical potentials are derived. Equivalence between chemical vs. mechanical load is discussed. Using the triphasic constitutive equations, it is shown that for every chemical load generated by a given concentration of polyethylene glycol (PEG) in a NaCl solution there corresponds an isotropic mechanical load, PA, which imparts to the tissue an identical equilibrium deformation. However, the mechanical load must be delivered in an isotropic manner via rigid-porous, free-draining loading platens.