Studies on solubilization of cod (Gadus Morhua L.) viscera at natural substrate pH are described. Viscera were hydrolysed by endogenous enzymes alone or in combination with one of seven different commercial protease preparations (Alcalase (R) 2.4L, Neutrase (R) 0.8L, Protamex (TM), Papain, Bromelain, Actinidin and a plant protease mix). Hydrolysis reactions were conducted with freshly thawed viscera utilizing an initial temperature gradient and terminated at various time points by heat inactivation of the enzymes. Hydrolysates were characterized with respect to soluble dry matter (DM), turbidity, concentration of alpha-amino groups and peptide molecular weight distribution. Alcalase and Papain gave the highest yields of solubilized dry matter, approaching 95% for hydrolyses with high concentrations of Alcalase. Interestingly, endogenous enzyme activity alone was sufficient for obtaining a solubilization yield of up to 75% (in terms of solubilized dry matter). Thus, the extra yield gained by adding commercial proteases is limited and may not always be beneficial, economically. (c) 2004 Elsevier Ltd. All rights reserved.