Foam fractionation of proteins is especially advantageous in treating dilute solutions where other separation methods run into economical limitations. Improvement in separation efficiency can be obtained by adding external reflux to the column. This work studied operational variables, such as superficial gas velocity and solution concentration, on the enrichment of the foam phase when external reflux was added to the separation. Bovine serum albumin, cytochrome C, and barley malt alpha-amylase were the proteins fractionated in a column 3.2 cm in diameter and 105 cm in height operated by bubbling nitrogen in pH-controlled solutions. The determination of solute enrichment and purification factor for several external reflux ratios demonstrated the importance of this operational variable on the efficiency of foam fractionation of proteins.