Protein hydrolysates inhibiting the angiotensin converting enzyme (ACE) in vitro, are potentially interesting constituents for blood pressure decreasing products. To minimise the amount of hydrolysate needed, the ACE inhibitory activity should be maximised. The total peptide composition of a hydrolysate determines its ACE inhibitory ability and depends on the specificity of the proteolytic enzyme and the process conditions used for the production of the hydrolysate. In the present research, the effect of process conditions on the ACE inhibitory activity of whey protein concentrate hydrolysed with a pancreatic enzyme mixture was investigated systematically using response surface methodology. It was shown that ACE inhibitory activity of the whey hydrolysates could be controlled by regulation of five process conditions. Hydrolysis conditions for optimal ACE inhibition were defined using a response surface model.