OBJECTIVE To determine whether Mycobacterium tuberculosis ribosomal RNA (rRNA) is present in fresh tissue specimens from patients with sarcoidosis. METHODS A prospective study. METHODS A university-based hospital. Patients Thirty-five patients diagnosed as having sarcoidosis at the University Hospital of Bellvitge, Barcelona, Spain, were included in the study. Fresh tissue samples with granulomatous inflammation were prospectively collected between 1997 and 2001 from all patients. For each sample tested, approximately 1 negative control was included. METHODS Mycobacterium tuberculosis rRNA was detected using an isothermal enzymatic amplification system of target rRNA of M tuberculosis complex via DNA intermediates. Smears for acid-fast staining and mycobacteriological cultures were also obtained. RESULTS A total of 78 biopsy specimens (57 skin, 10 lymph node, 3 lacrimal gland, 2 spleen, 2 lung, 2 muscle, 1 bone, and 1 nerve) collected from 74 patients (35 patients with sarcoidosis and 39 control patients) were included in the study. Stains for acid-fast bacilli and mycobacterial cultures were negative for organisms in all cases. Mycobacterium tuberculosis rRNA was not detected in the specimens from any patients with sarcoidosis or in those from control patients whose cultures were negative for organisms. Ribosomal RNA was detected in 6 tissue specimens from patients with cultures that were positive for M tuberculosis and that were processed in parallel to the samples included in the study. CONCLUSIONS Although previous studies have reported that mycobacterial antigens may play a role in granuloma formation in some patients with sarcoidosis, our results suggest that M tuberculosis cannot be considered to be the etiologic agent of the disease.