Severe postoperative wound infections caused by Nocardia farcinica were repeatedly observed in a German hospital surgical ward. A pulsed-field gel electrophoresis (PFGE) protocol was established to characterize the genetic relatedness of the bacterial isolates from these infections. All 18 isolates from postoperative infections that have occurred since 1985 belong to a common endemic genotype; organisms of this genotype were also detected in the air of two rooms of the department where these postoperative infections occurred. In contrast, two environmental isolates from another building on the same campus showed a distinct genotype. Three cases of pulmonary infections, at a department which is located in proximity to the surgical department, were also caused by the endemic type, which suggests aerogenic spread of the endemic strain to these patients. Controls consisting of epidemiologically unrelated isolates from sporadic infections in other towns belonged in each case to a different genotype. PFGE was well suited to differentiate various types of N. farcinica and revealed an endemic strain causing postoperative wound infections possibly after aerogenic transmission.