• The eyes of 20 patients with primary immunodeficiency syndromes were examined, and microbial cultures of their lids and conjunctivae were made. Nine patients had a history of recurrent external ocular infections, and six of these had active blepharitis or blepharoconjunctivitis at the time of examination. A single pathogenic bacterium was isolated from the lids and conjunctivae of six patients with a history of infection; a mixture of two possible pathogens was cultured from eyes of three other patients. Three of the nine patients with infections had impaired B-cell and intact T-cell immunity, whereas three patients had impaired B-cell and T-cell immunity. Two patients had chronic granulomatous disease in which a defect in phagocytosis was the predominant immunologic abnormality, and one patient (with mucocutaneous candidiasis) had intact B- and T-cell function at the time of testing. Although the immunodeficient patients had a higher incidence of lid or conjunctival infection than 20 age-matched controls, the microbial flora of the lids and conjunctivae did not differ between the two groups.