A study was undertaken to test the hypothesis that Staphylococcus aureus colonization of the lid margins could determine the expression of allergic eye disease in atopic patients. The authors compared lid isolates of S. aureus from 23 adults who had both atopic dermatitis and chronic conjunctivitis and isolates from 14 patients who had atopic dermatitis but who lacked ocular disease. No significant difference was found in either the staphylococcal protein A or hemolytic toxin production by isolates from the two disease groups, and there was no difference between groups in the quantity of serum IgG nor IgE antibodies to staphylococcal ribitol-teichoic acid. In seven patients with chronic allergic conjunctivitis who were challenged with staphylococcal protein A or heat-killed S. aureus, delayed-type hypersensitivity was not enhanced. These results suggest that although S. aureus colonization of the lids is common in atopic patients, neither the pattern of toxin production nor humoral or cell-mediated immunity to S. aureus play a role in the expression of chronic allergic conjunctivitis.