The shell vial technique for isolation of cytomegalovirus was adapted to detect Rickettsia conorii in blood culture using human fibroblast monolayers. The inoculation was performed with low speed centrifugation and the rickettsiae demonstrated by immunofluorescence 24-120 hr after inoculation. R. conorii was identified in 11 of 13 patients with Mediterranean spotted fever in 48-72 hr.