This is a prospective study recruiting 120 patients successively who were admitted to the chest department in hospital for respiratory infections irrespective of their aetiology. The aim of the study was to assess the frequency of nocardiosis in respiratory pathology in the era of AIDS and in an area where tuberculosis is endemic. The HIV serology was carried out on all 120 patients. A systemic search was made for nocardiosis and Koch's bacillus in the sputum and also in the broncho-alveolar lavage liquid obtained by endoscopy. The HIV serology was positive in 74 patients (61.7%). Pulmonary nocardiosis was diagnosed in five patients (4.2%), of whom four patients were HIV positive (80%). Tuberculosis was diagnosed in 58 cases (48.3%) of whom 40 were HIV positive (70%). The association of nocardiosis and tuberculosis was present in only one patient. The radioclinical aspect of nocardiosis in our service was suggestive of tuberculosis. The prevalence of nocardiosis in our series at 4.2% is in agreement with that obtained in autopsy studies in the Ivory Coast. The similarity of the radioclinical appearance between tuberculosis and nocardiosis demands that a search is made for the latter on all HIV positive patients and in negative cases a search for Koch's bacillus and empirical antibiotic therapy ought to have a spectrum of activity that would include nocardia.