Apparent diffusivities of bovine serum albumin (BSA) in bovine erythrocyte suspensions were measured over a range of cell concentrations and shear rates. The work had two purposes: to obtain further validation of a new method for measuring diffusion in suspensions, and to increase understanding of molecular transport in blood. Results were compared to long-standing but poorly validated models of molecular transport in suspensions. All models lacked predictive power; none firmly established the roles of fluid shear and particle volume fraction in determining solute diffusion; and one, the product of a widely quoted review appears to be fundamentally flawed. (C) 2010 Elsevier Ltd. All rights reserved.