The incidence of unclassified mycobacteria in the gastric contents of healthy employees and patients with pulmonary disease and in the sputum of patients was investigated. The incidence of these organisms in both employees and patients was reduced by refinements in technique of gastric aspiration. The incidence was the same in both groups using the same technique of collection. The data suggest a sporadic inconstant source of unclassified mycobacteria unrelated to tuberculosis or chemotherapy with no evidence to support the theory that these organisms are variants of Mycobacterium tuberculosis.