For detecting antibodies against the teichoic acids of Staphylococcus aureus (SA), a commercially available Ouchterlony double-diffusion procedure kit was chosen. Thirteen of 26 patients with chronic SA osteomyelitis, 2 of 2 with SA spondylitis and 5 of 6 with arthritis had a positive assay (58%) in contrast to 8 of 24 patients of the control groups (33%). High titers correlated well with the extent and duration of antigen presentation in the bloodstream for cells of representing the specific immunity. Localized infections with minor antigenemia elicited a detectable but weak antibody response.