A general formalism of nonequilibrium thermodynamics of multicomponent
fluids is given. Reversible parts of balance equations for the extens
ive variables are constructed in such a way that the growth rate of th
e extensive variables are related to their conjugate intensive paramet
ers in an antisymmetric manner. This enables us to give the balance eq
uation for the diffusional flow which plays an important role in the s
tudy of superfluidity and complex fluids.