A monospecific troop of Cercopithecus cephus was followed for five months using the radio-tracking method. Temporal and spatial distribution of the activities is described. Two peaks of locomotion are found in the first half of the morning and the second half of the afternoon. Phytophagy follows the same rhythm, while feeding on prey and resting increase at mid-day. Strong daily variations are shown in forest type usage according to the activity performed. The more open and tallest forest is chosen during the night and for fruit gathering, while the densest and lowest one is significantly preferred for resting. Parallel daily variations are found in the forest level usage : resting, insect hunting and social interactions occur at levels lower than locomotion and fruit gathering. The total time spent feeding does not differ between the age classes, however the time spent feeding on insects decreases with age while phytophagy increases. The young are found at significantly lower levels than the adults. The adult male stays higher than the other troop members, especially when resting. Inter-individual distances are lowest between females and young, while the adult male has a more peripheral position. Troop cohesion is higher at the end of the day. Physiological, behavioral and environmental constraints which might influence such activity rythm and differences between age classes are discussed.