ABSTRACT. Enzyme-linked immunosorbent assay (ELISA) was used for IgG antibody determination to teichoic acid and a-toxin from Staphylococcus aureus in 65 patients with cystic Fibrosis (CF). In patients chronically colonized with S. aureus, elevated titres to teichoic acid were found in 13/35 (37%) patients, to a-toxin in 12/35 (34%) and to either antigen in 18/35 (51%). Patients with elevated titres to teichoic acid had a significantly lower X-ray score than patients with normal titres. The highest titres against both teichoic acid and a-toxin were seen in patients not receiving optimal treatment. These findings suggest that staphylococci contribute to the tissue damage in CF and that the determination of antibodies especially to staphylococcal teichoic acid might be of value in the diagnosis and management of staphylococcal infections in patients with CF.