The authors give 4 observations, made in Rennes (France), of 3 cases contracted in France and 1 in Canada, cases they think to be related, for 3 at least, to the infectious entity described by American authors under the name of Lyme disease. If 1 of these cases was limited to an erythema chronicum migrans, the 3 others showed a beginning evolution towards a classical Lyme disease. In 2 of these 3 last cases, the infection was perhaps cut short by a quickly applied therapy by antibiotics. They discuss the different hypotheses about the negative Borrelia serologic reactions in 3 of the 4 cases. A possible arboviral aetiology is evocked. In only one of the 4 cases, a tick-bite can be asserted, the role in the the transmission of this kind of arthropods being strictly excluded in 2 of the 3 other cases (transmission likely by a mosquito and by a biting fly (tabanid?)). The authors put the question of the possibility of transmission, for erythema chronicum migrans and Lyme disease, by arthropods other than ticks.