The carnivorous nudibranch Roboastra tigris preys preferentially upon two nudibranchs,Tambja abdere and T. eliora, that in turn feed upon the bryozoan Sessibugula translucens. All four organisms contain tambjamines A-D (I-IV) that were shown to be fish feeding inhibitors. When attacked by Roboastra, T. abdere secretes a distasteful mucus containing a total of 3 mg of the tambjamines that sometimes causes the Roboastra to break off the attack. Under similar circumstances T. eliora attempts to swim away; it presumably contains insufficient of the tambjamines to deter Roboastra. Roboastra follows the slime trail of nudibranchs using contact chemoreception and reverses direction when the trail is broken. The slime trail ofT. abdere contains low concentrations of the tambjamines. In Y-maze experiments,T. eliora was attracted towards seawater containing S. translucens and seawater containing 10(-10) M tambjamines A and B (1∶1) but was repelled by seawater containing > 10(-8) M tambjamines A and B. At higher concentrations the mixture of tambjamines may be recognized as an alarm pheromone.