[en] Equine piroplasmosis is a tick-borne disease, the aetiological agents of which are either Theileria equi or Babesia caballi parasites. Piroplasmosis is commonly encountered in acute or sub-acute clinical forms although clinically recovered horses may remain asymptomatic but infected for several years. The clinical detection of such apparently healthy carrier horses (that serve as a host for subsequent infecting ticks), remains a worldwide challenge for controlling the spread of the disease. The aim of the present paper is to report on the detection of both T. equi and B. caballi by PCR in the bone marrow of naturally infected asymptomatic horses. Among 35 bone marrow samples evaluated for orthopaedic clinical research purposes, three samples from clinically healthy horses were found to be positive for T. equi, one of which was also positive for B. caballi. Even if the precise localisation of these parasites as well as the underlying mechanisms for persistence still remains unknown, one should not exclude bone marrow as a potential reservoir site for T. equi and B. caballi in infected asymptomatic horses. We suggest that, this possible localisation site (the bone marrow) should be considered as a therapeutic target when treating parasitic infection in apparently healthy horses.