Although the existence of Nocardia asteroides as a human pathogen in Mexico has been known for several years, up to now there are only few reports in our country concerning the isolation of this microorganism both as a saprophyte as well as human or animal pathogen. This fact is more interesting when compared with the high incidence of N. brasiliensis, causal agent of actinomycotic mycetoma, the most frequently observed deep mycosis in Mexico. In this paper, the isolation of eigth strains of N. asteroides from clinical specimens is reported. Five strains were isolated from sputa, one from a fistulous lesion of the scrotum, one from a brain abscess and one more from a foot mycetoma. One of the strains isolated from sputum was in a case of pulmonary nocardiasis; another of these strains was isolated from a patient with coexistent pulmonary tuberculosis and nocardiasis. With the last three strains isolated from sputa, it was not possible to establish any correlation between the isolations and the clinical and radiological findings of the patients; two of the patients had pulmonary tuberculosis and the isolation of N. asteroides was achieved only in one occasion in each case, with scant growth, and observed in routine cultures made for tubercle bacilli. The last strain was isolated from the sputum of a patient with chronic bronchitis. Some comments are made to the possibility that these three last isolations merely represent a saprophytic phase of the fungus. Some clinical and other features are discussed concerning the other three cases of scrotal fistula, brain abscess and mycetoma produced by N. asteroides. [ABSTRACT FROM AUTHOR]