Tests were conducted to evaluate the inhibitory effects of collagen peptides in the hydrolysate of sea bream scales on the activity of angiotensin I converting enzyme (ACE, EC3.4.15.1). The scales were hydrolyzed using an alkaline protease treatment by which 92% of the peptides were degraded to form hydrolysate. The 50% inhibitory concentration of the peptides was as high as 0.57 mg ml(-1). In addition, using spontaneously hypertensive rats, oral administration of 300 mg of the peptides (kg of body weight)(-1) d(-1) was shown to decrease blood pressure significantly (P<0.05). Four peptides that demonstrated high ACE inhibitory activities were isolated from the hydrolysate of the scales using chromatographic methods. The ACE inhibitory activities of the isolated peptides were 5-20 times higher than that of the unpurified hydrolysate. The amino acid sequences of inhibitory peptides were determined to be Gly-Tyr, Val-Tyr, Gly-Phe and Val-Ile-Tyr. (C) 2003 Elsevier Ltd. All rights reserved.