A total of 15 months were spent on field research in eastern Madagascar studying the largest extant lemur Indri indri. Social relationships were analysed according to the frequency and direction of affiliative and agonistic behaviours, and with respect to the relative tree positions and behavioural synchrony of group members. The relationship between the adult male and adult female in each group was distinguished by the sub-ordinance of the former. Between group variation in adults’ relationships are examined with respect to the function of this behaviour.