The extraction of lysozyme was studied using di-(2,4,4-trimethylpentyl) sodium phosphinate, R2POONa, and di-(2,4,4-trimethylpentyl) sodium dithiophosphinate, R2PSSNa. For a R2POONa reverse micellar system, all lysozyme was removed from the aqueous phase when the pH of the aqueous solution was set below the pi of the protein. The extraction of lysozyme into a R2PSSNa reverse micellar system was independent of the pH of the aqueous phase. A solubilization limit of lysozyme exists in the R2POONa reverse micellar phase. The lysozyme recovery was 70% from the R2POONa reverse micellar phase, and less than 10% from the R2PSSNa reverse micellar phase.