Antiproliferative activity of 18 fish protein hydrolysates was measured on 2 human breast cancer cell lines grown in vitro. Three blue whiting, three cod, three plaice and one salmon hydrolysates were identified as significant growth inhibitors on the two cancer cell lines. Preliminary analysis of hydrolysates composition evidenced they contained a complex mixture of free amino acids, peptides with various sizes ranging up to 7 kDa and in a lower proportion, lipids and sodium chloride. RP-HPLC fractionation of fish hydrolysates is currently undertaken to purify anticancer peptides, lipids or other bioactive trace compounds responsible for this antiproliferative activity. (c) 2005 Elsevier Ltd. All rights reserved.