1. Concentrations of six bromophenol-related compounds were determined in Thelepus extensus, T. setosus and T. cincinnatus from coasts of the Kerguelen Islands, Brittany, West Sweden and the Bransfield Strait. One compound, bis(3,5-dibromo-4-hydroxybenzyl)ether, has not been reported previously in Thelepus.2.The three species contained the same compounds in comparable concentrations. These were not related to animal wet wt. Total values ranged between 0.5 and 1.5 mg/g wet wt.3 Highest concentrations were found in the distal parts of worms, particularly in tentacles and in the end of the abdomen.4. Thelepin, an antimicrobial constituent, was detected in the distal parts only and is suggested to be of antiseptic importance in wound healing in the body parts that protrude from the worms' tubes.