EEG, sleep-waking organization and phasic sleep activities (PGC) were studied in 6 adult female Papio anubis with chronically implanted electrodes and partially constrained. Papio anubis shows a well characterized sleep (besides an individuality peculiar to each baboon): short sleep latency (18 +/- 14 min), very brief REM latency (5 +/- 5 min), stable stage 1 (86 +/- 11 min), REM duration with little variation (70 +/- 15 min) and abundant deep sleep (stage 4 = 79 +/- 44 min). Geniculate spikes, in general biphasic, occur in great number in this species: 34,778 +/- 7355 per night (44.6% of them in REM). The frequency of spike discharges per minute in REM reaches a mean of 218 +/- 10. In true slow sleep (SS 1), 4--5 spikes per group prevail; in slow sleep followed by a REM episode (SS 2), 6--10 spikes per group are the most numerous. REM is characterized by groups of 6--10 or more spikes. Several specific features are seen: (1) alternation and/or asymmetry of the bursts from the 2 lateral geniculate (LG) nuclei during SS 2 and REM, tendency towards symmetry in SS 1; (2) inversion of spike polarity in the lowest LG layers; (3) variation in spike form from one instant to another and from one LG to the other; (4) presence of spikes in the optic tract. At the cortical level, PGC phasic activities resemble the 'saw tooth waves' described in man. The PGC activities of various primates, and particularly of Papio anubis, seem, by their complexity, to reflect a more elaborated evolution of this particular phenomenon of sleep and differ from those of cat. The monkey lends itself, hence, as a better model for any extrapolation to man. Finally these results raise the question of species within a single genus.