With new techniques for culturing blood, mycobacteremia is diagnosed with increasing frequency. Patients with the acquired immune deficiency syndrome, in particular, are prone to infection with Mycobacterium avium-intracellulare, and blood culture for this organism is a useful way of diagnosing infection and following response to treatment in these patients. The Isolator (DuPont Co.) has already been demonstrated to be useful in diagnosing mycobacteremia. Recently Johnston Laboratories has developed a new mycobacterial blood culture medium. As many diagnostic microbiology laboratories use the BACTEC system, it would be convenient for them to be able to use this system for mycobacterial blood culture as well as for routine blood culture. We will be comparing the newly-developed BACTEC medium with the Isolator Procedure for the detection of mycobacteremia.