Multiple binding of laurate (n-dodecanoate) to human serum albumin was studied by a kinetic dialysis method. With this method the concentration of unbound ligand can be determined by measuring the rate of exchange of radioactive label across a dialysis membrane under conditions of equilibirium.Determination of the rate constant of exchange, in the absence of albumin, revealed that laurate does not change its state of aggregation over a concentration range from 0.1 pM to 500 pM, indicating the prevalence of a monomer.Binding of laurate to albumin, at pH 7.5, 37"C, was investigated through 220 determinations of binding equilibria in the range of 0-10 mol laurate/mol albumin, corresponding to a concentration range of unbound laurate from 1 nM to 0