SummaryOul of 11 patients suffering fromMycobacterium xenopilung disease, 9 were treated with an empiric antituberculous triple chemotherapy until specific identification and antibiogram were available. Despite the important“in vitro”resistance to drugs, most of the patients improved; in the other patients, the impairment was always due to the underlying pathology. Wc conclude that the“in vivo”response of M.xenopiinfections to antituberculous drugs is little influenced by the“in vitro”sensitivity.