A male, a female, two juveniles and two cubs of European otter Lutra lutra were filmed in a large enclosure during a period of 8 months. For each episode of acoustic communication, data were collected on uttered sounds, involved individuals, and their distance, postures and behaviour before, during and after vocalizing. Eight different sounds were considered, according to the inventory referred by Rogoschik (Wiss. Beitr. Univ. Halle, 37(1989): 213-221). Associations between the recorded parameters were evaluated by an association index. The male and female vocalized frequently towards the cubs and human beings, and cubs towards the female. Senders and addressees were found to be unequally distributed for the different sounds. Vocalizations occurred preferentially on land and along the banks. The most frequent behavioural contexts were parental contacts (between the female and the cubs), contacts with human beings and playing activity; on the other hand, vocalizations rarely occurred while fishing, moving, feeding and marking. Hiss and snort were uttered when an animal approached the addressee, from a distance of a few meters; they were often accompanied with a typical arcuated head movement. Moan was a threat sound, uttered while keeping the body motionless and fixing its eyes on the addressee. Chuckle, chuckle-chitter, chitter and squeal were mostly uttered at very short distances; although they all show a similar "staccato'' acoustic structure, only the chuckle was uttered in social contexts, while the other ones were associated with increasing aggressive excitement. Whistle was uttered usually in very long sequences, at long distances; its main function seems to be keeping an acoustic contact between individuals, in particular cubs and their mother; however, sometimes it was uttered by juveniles together with chitter and other agonistic sounds. This shows that the communicative system of the species is quite complex.