The biodistribution and kinetics of a receptor-binding hepatic radiopharmaceutical, Tc-99m-galactosyl-neoglycoalbumin (Tc-NGA), were investigated using mammalian and avian models. The radiopharmaceutical exhibited four significant features associated with receptor-mediated binding at the hepatocyte membrane in mammals: (a) high tissue specificity, (b) high molecular specificity, (c) affinity-dependent uptake, and (d) dose-dependent uptake. Diminished hepatic uptake by the avian model illustrated low nonspecific binding. The kinetic sensitivity to ligand-receptor affinity and stoichiometry illustrated the principal feature of receptor-binding radio-pharmaceuticals, namely, quantitative assessment of tissue function based upon the biochemical interaction of a ligand and its specific receptor.