A process for enzymatic hydrolysis of proteins to synthesize biologically active peptides in an aqueous two-phase system is proposed. We apply this method to the enzymatic hydrolysis of zein (corn protein, Zea mays L.). Zein and its enzymatic hydrolysates distribute to PEG-and DEX-rich phases, respectively, in an aqueous PEG/DEX two-phase system. The angiotensin I converting enzyme (ACE) inhibitory peptides are recovered in a DEX rich phase.