A theoretical model, appropriate for data interpretation, is presented for the transcapillary fluid exchange and associated intraluminal hydrodynamic and solute transport occurring in the microocclusion of single capillaries. This analysis describes the spatial and temporal behavior of the intraluminal flow. A comparison of the theory with in vivo data suggests good qualitative agreement with that data and, further, the specification of filtration parameters in the model leads to good quantitative agreement regarding the displacement histories of erythrocytes. The model includes both natural and tagged colloidal osmotic influences and can, therefore, be used to represent experiments wherein the concentration of a dyed colloid is measured and related to fluid filtration. The relative merits of measuring colloidal concentration or erythrocyte displacement are discussed within the context of the model.