Three hydrolysates made from cod viscera by different enzymatic hydrolysis procedures were tested as a combined source for nitrogen, amino acids and vitamins in microbial growth media. Using a panel of five different microbes: Escherichia coli, Bacillus subtilis, Lactobacillus sakei, Saccharomyces cerevisiae and Aspergillus niger, the performance of these viscera hydrolysates was compared to the performance of common commercial peptones in an automated growth analyzer (Bioscreen Q. The results show that the fish hydrolysates in general are promising alternatives to currently available commercial nitrogen sources of other origins. In the case of the food-grade and nutritionally fastidious L. sakei, two of the fish hydrolysates were clearly superior to all tested commercial peptones. For several microbes, the choice of the proteolytic enzymes used to produce the fish hydrolysate had considerable impact on performance of the resulting hydrolysate, both in terms of maximum growth rate and biomass production. In terms of hydrolysate performance, the generally best enzyme for production of a fish peptone from cod viscera was found to be Alcalase. (c) 2005 Elsevier Ltd. All rights reserved.