Abstract: A method of separating a soluble milk component from milk is disclosed. The method involves the use of tangential flow filtration across a membrane to form a retentate and a permeate, combining the permeate with the original milk sample, and repeating this procedure until the milk has been sufficiently purified. Preferably, the milk is combined with a chelating agent, such as EDTA, to improve the purification efficiency. This procedure is advantageously employed with milk from transgenic animals which have been genetically altered to express exogenous proteins, such as therapeutic proteins, in their milk.