In a survey dealing with the frequency of onchocerciasis in leprous environments in the Marchoux Institute in Bamako (Mali) evidence is given that 43% of the leprous persons hospitalized there were touched in addition by onchocerciasis whereas, only 14% of the consultants in dermatology have proved to be also onchocercian. This last frequency is consistent with the overall estimation usually recognized for Mali. No difference was shown between leprous and non-leprous persons for snip. In contrast, 33% of microfilariae bearing leprousians showed no positive reaction to diethylcarbamazine whereas no more than 5% of non-leprous persons displayed similar negative response. Similarly leprousian blood yielded most often the microfilariae of Onchocerca volvulus. Surprisingly, hypereosinophilia has proved to be normal or null in 37% of microfilariae bearing leprosians. Though aware of the occurrence of numerous real or possible biases in such an approach the authors wonder what meaning such a difference between leprous populations and non-leprous ones in Mali can have. If a relation is definitely borne out in the future between both pathologies, they further wonder whether leprosy is the bed of onchocerciasis or vice versa.