Activities and social interactions of male and female termite replacement reproductives were compared in an ethogram type investigation performed on representative colonies of Kalotermes flavicollis. Our observations suggested a sex-based behavioural specialization between the two reproductives, with the male being the one to show the greatest frequency of movements in the nest, vibratory acts, and frequency and variety of social contacts. Apart from being important for the periodical insemination of the queen the king appears to hold a basic role in the social structure and dynamic development of the colony as a intermediary in social interactions between the queen and the other colony members.