SummaryWe describe two cases of serious iatrogenic infection caused by rapidly growing acid-fast organisms of theMycobacterium fortuilum-cheloneicomplex. The first was identified asM. J’ortuilumand caused a deep infection of a total hip prosthesis in a 77-year-old man. Recovery was obtained by removal of the prosthesis, drainage and parenteral antibiotics. The second, identified asM. cheloneiwas isolated from a 14-month-old boy and caused subcutaneous abscesses at the site of human immunoglobulin injections given for agammaglobulinaemia. The literature ofM.fortuitumandM. cheloneiinfections is briefly reviewed and simple tests are recommended to separate the two species.