One hundred six eyes of 53 patients with severe thermal burns were studied with serial conjunctival cultures during a four-month period. A dramatic shift of the normal conjunctival flora from the preponderance of Staphylococcus epidermidis and Corynebacterium to S aureus and Gram-negative bacilli was observed. This commonly occurred on the fifth to sixth postburn day and represented colonization of the conjunctiva by bacteria recovered from other sites in the body. Despite the high incidence of Pseudomonas aeruginosa isolates (34%) of these eyes, deleterious effects were noted in only three eyes in two patients in whom infectious corneal ulcers developed before these patients died.