A search for antibacterial activity in different body parts of the green sea urchin Strongylocentrotus droebachiensis, the common starfish Asterias rubens, and the sea cucumber Cucumaria frondosa was conducted. Antibacterial activity was detected in extracts from several tissues in all species tested, but mainly in the coelomocyte and body wall extracts. Relatively high antibacterial activity could also be detected in gastrointestinal organs and eggs from A. rubens and in eggs from C. frondosa. Differences between active extracts regarding hydrophobicity and sensitivity to heat and proteinase K treatment indicated that several different compounds were responsible for the antibacterial activities detected. Lysozyme-like activity could be detected in several tissues from A. rubens. Haemolytic activity could be detected in all species tested, especially in the body wall extracts. Results from the current study suggest that marine echinoderms are a potential source for the discovery of novel antibiotics.