Patients (305 patients with pulmonary tuberculosis) and controls (290 household genetically unrelated contacts) were tested by polymerase chain reaction (PCR) for polymorphisms in the intron 15 and the 5' untranslated region of the gene coding for the a3 isoform of the human ATPase gene. Diagnosis of pulmonary tuberculosis was based on chest radiography and sputum smear examination and confirmed by PCR and bacteriological tests. Alleles (two at each site) segregated in the form of four haplotype pairs: 13, 14 (very rare), 23, and 24. The 13/24 (double heterozygous) patients were protected against tuberculosis (OR: 0.15; P: 10(-8); CI: 0.08-0.3). The 13/13 vs 13/24 and 23/23 vs 23/24 (double homozygous) patients were susceptible to the disease (OR. 5.8; P: 6 x 10(-7); CI: 2.8-11.9; OR: 4.5; P: 5 x 10(-7); CI: 2.5-8.4, respectively).