The dispersion of solutes during blood flow through a straight tube.

1. The dispersion of solutes in plasma and blood has been studied by observing the clearance at a point down-stream of a bolus of labelled solution by the steady flow of unlabelled solution.2. With a low molecular weight solute the clearance curve is qualitatively similar in 2N-KCl solution, plasma and whole blood.3. The dispersion of a high molecular weight protein, [(131)I]HSA, in plasma is dominated by the velocity profile of the flow.4. The clearance curves for HSA in whole blood are similar to those of plasma, except that the red blood cells speed the clearance of protein in the tail region of the curve.5. An analysis of the data suggests that the dispersion of solutes during blood flow through a straight tube can be attributed to the combined effects of solute diffusion and laminar convection. There is no evidence that induced motion of the erythrocytes produces significant mixing, in the bulk of the flow.