Community participation in the control of tropical diseases is of major importance nowadays, particularly for sleeping sickness (Gambian trypanosomiasis). Indeed, the authoritarian measures used with success to control this disease during the colonial period are difficult to apply now. Moreover, in the Congo, cultural and financial restrictions are such that patients sometimes refuse treatment. Thus, it has become highly desirable for vector control to be carried out at the same time as the treatment of patients. Trapping tsetse flies (or Glossina) is an ingenious and effective anti-vectorial method which has been tested in 55 villages of the Congo. The blue-black pyramid trap used does not require insecticide impregnation, and is hung in the branches by means of a capture-bag containing diesel oil. These trials, conducted in the sleeping sickness focus of the Niari river, have demonstrated the feasibility of local communities taking over the responsibility for the traps, while at the same time revealing certain obstacles. Indeed, the efficacy of this method depends on the optimization of trapping. This involves the determination of strategic capture sites by periodically harvesting the flies and moving the traps in order to catch the maximum number of flies. It also involves regular maintenance of the traps (i.e. repairs, checking the capture bag, clearing vegetation...). However, although these activities would appear to be feasible at community level, they are not always carried out satisfactorily. This results in the insufficient viability of the traps and finally to the reinvasion of the treated area by the tsetse. This study presents aspects of the present-day Congolese socio-cultural environment characterized by the revitalization of traditional Bantou mysticism and religious worship. The possessors of the 'Vital Force' or Kundu (sorcerers and healers) are confronted at night in an 'over-reality' consisting of the visible reality together with innumberable beings and objects existing specifically in the invisible state. This nocturnal confrontation may modify the local balance of power and relationships, and is also thought to cause certain symptoms of sleeping sickness and other diseases. During the colonial period, Kundu was prohibited. Under the influence of the Christian church, and because of the progress of modern medicine, the power of the sorcerers and healers gradually decreased. Then, in the 1960s, the eruption of Marxism as an anti-religious theory, modified the balance of power once more.(ABSTRACT TRUNCATED AT 400 WORDS)