The results of a study on the abundance of Amblyomma variegatum in different ecological zones and of Cowdria ruminantium infection rates in nymphal and adult ticks of the North Guinean zones are given. Joint research is also conducted on the evaluation of seroprevalence. In this study, it appears that the vector is most important in the North Guinean zone, followed by the South Sudan and the coastal Niayes zones. Elsewhere, the tick populations are not significant or absent. The infection rate in the North Guinean zone is high: 1.1% at least for adult ticks and 7.8% for nymphs. The seroprevalence in the North Sudan and the Sudano-Sahelian zones is very low in the hinterland whereas the values are higher near the coast.