The vocal repertoire of talapoin monkeys consists of eleven basic vocal types within which 31 different sounds are described, including all intermediates, "lip-smacking" and branch noises (linked with cohesion calls). Calls are of short duration (1/20s to a few seconds). Some of them have a daily rhythm of emission. Their intensity is variable, the call range varying accordingly from a few to several (more) hundred meters. Talapoin calls are composed either of low-pitched structures, of high-pitched ones, or an association of the two. Seven calls, of the eleven basic types possess low-pitched components (pitch = 0.5 to 1KHz) giving them a common quality, constituting what may be called the "talapoin voice". Two graded systems have been described. One, the most graded, is composed of the aggression-flight vocal types; the second is linked with group cohesion. The important level of gradation within the vocal repertoire of this forest species contradicts the classical concepts which ascribe a "discret" repertoire to monkeys living in a closed milieu. The gradation of the vocal system of a species may be related more to an abundance of social contacts than to the structure of the milieu (multimodality of signals exchanged over short distances). During ontogeny, the vocal repertoire changes in both type and frequency of use. The structural modifications are either continuous, with the growth of individuals, or discontinuous with the sexual maturity of males. Under conditions of average excitation, differential call distribution and their relative frequency according to different individual classes lead us to generalize that the vocal behaviour of a particular class in a group (age, sex and social status) always differ qualitatively and quantitatively from that of other classes. Under conditions of high excitation, differential call distribution and their relative frequency according to different individual classes, lead us to generalize that any individual can give any call type when submitted to adequate stimulation. This difference between the real potentiality of a given individual and actual use in the wild is essentially related to the change of stimulating context as the monkeys grows older. In order to vocalize, the talapoin must receive stimulation which increases its excitation level and directs its response. Furthermore the excitation level does not directly determine a particular vocal type. The vocal response varies according to the situation and is adapted to the stimulus context. We distinguish between stimuli which propagate calls within a social group from those initiating calls. The former are essentially calls of congeners, the latter are more often visual, visual auditory, auditory then tactile. The majority of talapoin calls control the spatial distribution of the troop members in relation to external events (cohesion calls system, aggression-flight calls, mother-young contact calls). Choruses however have a more complex social role which is not completely understood. With a maximal energy concentrated arotmd 0.9KHz, the "lost" calls of young seem to be adapted to penetrate the forest milieu. The presence in certain calls of high-pitched components appears to be linked principally to the rise of the excitation level of the vocalizers. With eleven vocal types, the talapoin has a repertoire comparable to that of other monkeys. It is sympatric with Cercopithecus nictitans, C. cephus, C. pogonias and C. neglectus with which it shares a number of functional categories of calls, features probably imposed by forest conditions (poor visibility, winged predators, ...) examples are the cohesion system, dispersion calls, aggressive alarm to birds). Conversely, the physical structure of calls of genus Miopithecus and Cercopithecus have little in common. The frequent choruses in talapoin seem to be related to a more complex social life than that of the Cercopithecines. The talapoin is differentiated strongly from the sympatric species in the absence of loud calls, the specific characters of call structures and their more graded nature. A similar degree of differentiation is found in the morphological, physiological and eco-ethological traits characterizing the talapoin (GAUTIER-HION, 1970, 1971 a, b). Although some talapoin calls are higher-pitched than those of macaques, there are affinities between the vocalizations of talapoin and macaques : both have graded call systems arising in aggression-flight behaviour and there are similarities in calls with tonal structure: types 2 of talapoin; clear calls of M. mulatta (ROWELL & HINDE, 1962); "coos" and "high-pitched musical notes" of M. nemestrina (GRIMM, (1967); "coos" of M. speriosa (BERTRAND, 1969); "coo sounds" of M. fuscata (GREEN, in press). Finally, there is a close structural resemblance between the "lost" calls of infants talapoin and rhesus.