For isothermal isobaric diffusion in ideal associated solutions it is shown that the diffusional fluxes of the various solute components i, Ji, are given by Ji=–grad D*iCi where Ci is the concentration of component i in moles per unit volume and D*i is its self-diffusion coefficient. This result follows if (a) aggregate monomer equilibrium is maintained when diffusion takes place, and (b) the diffusional fluxes of the various aggregate species, r, are given by Jr=–Dr grad Cr, in accordance with Fick's first law or (c)Jr=–grad DrCr where Dr is the self-diffusion coefficient of species r.