A method is presented for the determination of the rates of movement of macromolecules into and out of specific tissues by analysis of the serum and tissue concentrations of the intravenously injected labeled macromolecule. Transfer rates of albumin into and out of rabbit aorta, skin, tendon, sclera, and cornea are given. These rates, and the steady-state ratios of tissue albumin to serum albumin, are interpreted in terms of current theory regarding the diffusion and filtration of albumin at capillary and lymphatic exchange sites in the tissues. Transfer rates for average body tissue, obtained by analysis of the serum concentration of intravenously injected labeled albumin, are compared with the transfer rates for the specific tissues studied.