Liver cell recruitment (the equivalent of capillary recruitment in other organs) was explored by carrying out multiple indicator dilution experiments with labeled rubidium across the liver of the anesthetized dog under basal conditions and after bleeding with saline replacement infusion, which increases liver blood flow. A mixture of 51Cr-labeled red blood cells (a vascular reference), 22Na (which immediately equilibrates in the extracellular space, the sum of the sinusoidal plasma and Disse or interstitial spaces, the expected distribution space for labeled rubidium in the absence of cellular entry), and 86Rb was injected into the portal vein, and normalized outflow patterns, expressed as outflowing fractions of each injected tracer per milliliter versus time, were obtained. In relation to the labeled red blood cell curve, the labeled sodium curve is displaced by flow-limited distribution into the Disse or interstitial space; it is lower on the upslope, reaches a lower and delayed peak, and decays more slowly. The early part of the labeled rubidium curve lies within the labeled sodium curve; it reaches a much reduced peak, and the later return of tracer entering cells is so slow that it is obscured by recirculation. Modeling of the concentrative cellular uptake of rubidium from the Disse space provided an influx permeability surface area product for labeled rubidium. This increases with flow over the observed flow range, demonstrating that sinusoidal recruitment occurs with increase in hepatic blood flow.