The authors describe in bulk, with the support of some maps, the main traditional groups of foci in Zaïre, extreme situations compared with the period 1930-1987. They indicate the distribution of glossinae according to the ultimate knowledge, as well as the evolution by groups of foci of sleeping sickness endemic for the last 10 years. Based on the most commonly accepted hypothesis, they explain the heterogeneous distribution of the active foci despite the omnipresence of glossinae, the low prevalence usually met, and why outbreaks occurred. Taking into account the actual development of the biochemical, immunological and biological technics as well as the fact that Zaïre, important endemic area, has not been yet correctly studied in such a field, the authors call for deeper epidemiological research.