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Serum samples from 20 patients with tuberculous pleural effusion (Group I), 20 patients with exudative pleural effusion due to causes other than tuberculosis (Group II) and 20 healthy controls were assayed for IgG antibody to PPD-298 by ELISA technique. A significant difference in the antibody titres was found between the Group I and the other groups. There were two false negatives in the Group I and one false positive result each from the Groups II and III. The technique was found to be highly sensitive and specific for the diagnosis of tuberculous pleural effusion.