The hydrodynamic equation D/T=alpha eta(beta), where D is the infinite dilution binary diffusion or self-diffusion coefficient, T is the temperature, eta is the fluid viscosity, and alpha and beta are constants, were demonstrated to be effective for predicting both binary diffusion and self-diffusion coefficients in high density fluids, i.e. liquid and supercritical states. When a solute was specified, the correlation well represented both binary diffusion and self-diffusion coefficients, irrespective of solvent over a wide solvent viscosity range. The solute-dependent constants alpha and beta were determined for 12 solutes with average absolute deviation of 6.2% for 1006 data points. (C) 2008 Elsevier B.V. All rights reserved.