Hydrolysates of whole bovine plasma and its separated proteins, albumin and globulins, which inhibit the angiotensin I converting enzyme (ACE) were prepared by enzymic hydrolysis with several proteases available for industrial use. Alcalase produced ACE inhibitory peptides from plasma proteins most efficiently and the Alcalase hydrolysate of albumin showed the most high activity (IC50=0.56 mg/ml). Sequential ultrafiltration of the hydrolysate with MW cut-off 10 000, 3000 and 1000 resulted in increased activity of each filtrate up to IC50 of 0.12 mg/ml. Sephadex G-25 gel chromatography of the hydrolysate eluted a peptide fraction below MW 1000 of the most potent activity (IC50=0.09 mg/ml). The hydrolysate was compared with the tryptic hydrolysate of casein considering the practical production of a functional food material in industry. The former was found to be more advantageous to separate the purified peptide fraction by industrial processes.