The immune response to mycobacterial antigens of 65 patients with pulmonary tuberculosis was studied using delayed skin test reactions and enzyme-linked immunosorbent antibody assays. Evidence for a spectrum of immune response was found. Six of 35 patients studied during the first month of therapy had tuberculin skin test anergy. Anergy was not related to state of nutrition or extent of disease, but it may have been associated with radiographically acute disease. The 6 anergic patients had somewhat higher antibody titers to mycobacterial protein, but not polysaccharide antigens, than did nonanergic patients.