The vocal repertoire of the little brown bat, Myotis lucifugus, was compiled through field studies of vocalizations and their behavioural contexts. Mating and hibernation were observed at an abandoned mine and feeding, maternal and night roost behaviours were studied at several sites. A total of ten call-types was distinguished, including echolocation pulses which may be used in social and orientation contexts. The remaining vocalizations were given in three main contexts: agonistic, mating and mother-young interactions. Four calls, including three audible, broad band ones, are associated with both inter- and intra-specific agonistic situations, and may form a graded continuum. Two vocalizations are used in mother-infant reunion and identification. A very discrete call, emitted by the male during copulation, likely serves as a pacification signal directed towards the female. This is one of the few reported discrete, situation-specific mammalian vocalizations. The size of the vocal repertoire of M. lucifugus is small when compared to other species of mammals, a fact probably related to the simple social system typical of this species.