A commercially available dot immunoassay that employs the lipoarabinomannan antigen was evaluated for the serologic diagnosis of tuberculosis. The test showed a high specificity (100%); however, its sensitivity was low (18.5%). Antibodies to lipoarabinomannan were detected in the sera of 7 of 71 patients with newly acquired tuberculosis and in sera of 10 of 21 patients with relapse tuberculosis. It has been shown by others that sera from patients with relapse tuberculosis had a higher concentration of antibodies and reacted with a greater variety of antigens (native culture filtrates of Mycobacterium tuberculosis H37Rv) than did sera from patients with newly acquired tuberculosis. Our data confirm the results of these previous studies as far as lipoarabinomannan is concerned. We conclude that the differences in the production of antibodies shown by the two groups of tuberculous patients (new and relapse) must be taken into account when assessing the usefulness of serologic tests for the diagnosis of tuberculosis.