During the period 1965-79 191 cystic fibrosis patients have been treated with 2349 course of anti-staphylococcal chemotherapy in the Danish Cystic Fibrosis Centre. The standard treatment was orally administered Fusidic acid in combination with Oxacillin or Dicloxacillin given for 14 days. In cases of penicillin allergy Fusidic acid in combination with Rifampicin was given. The overall results showed that S. aureus was eradicated from sputum by a single course of chemotherapy in 74% of the cases, although in 8% the original strains (phage-type) was replaced by a new strain. Repeated or extended treatment was successful in most of the remaining cases and, as a result, only 9% of our patients harboured S. aureus continuously for 6 months or more. On the average each patient received 2 anti-staphylococcal treatment per year, but no decrease in efficacy of repeated treatment was seen. Likewise, no significant increase of S. aureus precipitins and no development of resistant strains was seen in our patients. Due to the efficacy of chemotherapy and the principles of early treatment whether there are clinical symptoms of infection or not, S. aureus infection is now considered a minor problem without relation to poor prognosis in our cystic fibrosis patients.