A review of 573 cases of ulcerative keratitis cultured at the Bascom Palmer Eye Institute from January 1977 through September 1982 showed that 118 cases (21%) were associated with contact lens wear; of these, 64 were culture-positive. Of these culture-positive cases, 50 (78%) were caused by gram-negative bacteria, nine (14%) by gram-positive organisms, and two (3%) by fungal organisms. Of the 264 culture-positive ulcers not associated with contact lens wear, 119 (45%) were caused by gram-negative bacteria, 74 (28%) by gram-positive organisms, and 63 (24%) by fungal organisms. These statistically significant differences suggested that the organisms associated with ulcerative keratitis within our geographic region are modified by contact lens use. Pseudomonas was the organism most frequently isolated from ulcers associated with contact lenses and was responsible for nearly two thirds of the culture-positive cases.