Mycobacterium xenopi was cultured from a portion of surgically resected lung of an asymptomatic patient who had a renal transplant. The patient was receiving azathioprine and prednisone for the prevention of transplant rejection, as well as treatment for previously diagnosed pulmonary tuberculosis. M. xenopi infection was recognized as a second mycobacterial infection. The role of M. xenopi as an opportunistic pathogen in the compromised host is emphasized.