A review of Nocardia isolates at two Kansas City hospitals from 1968 to 1976 revealed isolates from 42 different patients. Data were available for analysis from 36 patients. According to strict criteria, only 17 (47%) were infected. Infection increased from zero to one yearly from 1968 through 1973 to five and seven in 1974 and 1975, respectively. Commensal isolates varied from zero to five yearly with no recent increase. Analysis of underlying disease and predisposing factors suggests that bronchopulmonary abnormalities predispose to colonization but infection is unusual without immunosuppression. Primary nocardial infection without known underlying disease accounted for only 4 of the 17 (24%) infections. Fever and leukocytosis were not helpful in distinguishing nocardial infection from colonization. A history of prior steroid use and a smear showing gram-positive filamentous organisms correlated highly with infection. Mortality correlated with pulmonary and brain involvement, prior use of steroids, and inappropriate therapy. Nosocomial infection was noted in five patients with a mortality of 60%. Overall mortality was only 29%.