Local motions of suspended particles or droplets can augment molecular diffusion and govern the transport of solutes in flowing dispersions. An electrochemical technique was developed for measuring the rates of augmented transport of solutes in a direction normal to the bulk flow through erythrocyte suspensions in Couette flow. Human, bovine, and rabbit erythrocytes in the form of normal, hardened, and ghost cells at volume fractions from 0.1 to 0.4 were studied at shear rates up to 3680 sec −1. Augmentation is defined as ( D e D s − 1) × 100% , where D e and D s are, respectively, the effective diffusivities in flowing and stationary suspensions. The augmentation is correlated with a characteristic Péclet number, a 2 γ/ D sF, where a is the effective radius of the particle, γ is the shear rate, and D sF is the Fricke's diffusion coefficient. The data are well described by A = αPe β in the Pe range from 4 to 100. The values of α and β depend on particle volume fraction φ and rigidity. The augmentation, however, does not change significantly between φ = 0.2 and 0.4. For suspensions of normal human erythrocytes at a volume fraction of 0.4, the augmentation is well described by A(%) = 6.1 Pe 0.89. This correlation agrees with all the reported experimental evidence of transport of heat, urea, albumin, and platelets in flowing blood. The correlations for hardened erythrocyte suspensions are also in agreement with the results on transport of heat, helium, and sodium chloride in flowing suspensions of rigid microspheres. Particle deformability does not affect the augmentation significantly at φ = 0.1 or less. For more concentrated suspensions, normalized augmentation increases with φ for suspensions of hardened erythrocytes, whereas it decreases with φ for suspensions of normal and ghost erythrocytes. It is inferred from this result that at φ > 0.1, multiplet collisions are important for augmentation for suspensions of rigid particles, whereas membrane rotation and deformation is the dominant mechanism for suspensions of deformable particles. The results also indicate that transport of macromolecules is significantly enhanced in flowing blood. For example, in flowing blood at a shear rate of 500 sec −1, the augmented transport rate of lipoproteins with a D s = 10 −8 cm 2/sec is about 100-fold of the Brownian diffusion rate.