ELISA has been used for the detection of IgG antibodies against PPD in 48 patients with pulmonary tuberculosis, in 10 individuals with previously treated tuberculosis and clinically recovered, in 22 PPD skin-test positive healthy volunteers and in 48 blood donors with unknown PPD skin-test. Positivity was obtained in 29 patients (83%) with active tuberculosis, in one patient (10%) with clinical recovery, in none of the healthy controls. This technique may have a potential diagnostic relevance in evaluating patients with suspected pulmonary tuberculosis.