Summary We did choose 100 sera from 917 patients who had suffered from tick-bite and/or erythema chronicum migrans and/or neurologic syndroms, thus who could have presented a Lyme's disease and for whom arbovirus serodiagnostic had been performed. Of these 100 sera, 23 had high antibodies titer for Borrelia burgdorferi. Of these 23 patients, 11 did answer to a questionnary. From these 11 patients, 5 had probably not been contaminated by Borrelia burgdorferi, one had a venereal syphilis, and 5 had certainly suffered from a Lyme's disease. Moreover, one of these 5 last patients presented antibodies against Eyach virus, which is, as Borrelia burgdorferi, transmitted by lxodes ricinus tick.