In 11 of 35 clinically proven cases of sarcoidosis, we detected DNA sequences coding for the mycobacterial 65-kDa antigen. In four cases, the sequences were homologous to Mycobacterium avium; seven sequences were related to other nontuberculous Mycobacteria. The insertion sequence 1110, characteristic for Mycobacterium avium, was present in three cases. The insertion sequence 6110 of the Mycobacterium tuberculosis complex (M tuberculosis, africanum, bovis, BCG) was not detectable in any of the 11 cases, ruling out the presence of members of the Mycobacterium tuberculosis complex. Therefore, it seems reasonable to speculate about a mycobacterial cause in some cases of sarcoidosis.