On the basis of the numbers of Nocardia strains referred to the National Reference Center for Mycoses and Antifungal Agents (NRC), Institut Pasteur, Paris, in the period from 1987 to 1990, it was estimated that between 150 and 250 cases of nocardiosis are diagnosed in France each year. A total of 63 clinical isolates were referred to the NRC and identified as Nocardia asteroides (66.7%), Nocardia farcinica (23.8%), Nocardia brasiliensis (3.2%), Nocardia otitidiscaviarum (4.8%) and Nocardia carnea (1.5%). Nocardia asteroides accounted for 71.4% of pulmonary infections, 80.0% of central nervous system infections and 80.0% of systemic infections. Patients infected with Nocardia farcinica died in 57.1% of cases, compared with 17.6% of patients infected with Nocardia asteroides. Corticosteroid therapy represented a significant factor in mortality. Isolates of Nocardia asteroides revealed variable resistance, whereas isolates of Nocardia farcinica were resistant to most antimicrobial agents. Only amoxicillin/clavulanic acid, imipenem, cefoxitin, kanamycin, amikacin, minocycline and vancomycin showed activity against both species. Nocardiosis caused by Nocardia farcinica may be a growing problem because of the relatively high incidence in AIDS patients and the resistance of this species to most antimicrobial agents.