Uniformly severe corneal infections were produced in guinea pigs by intracorneal injection of about 10 viable Pseudomonas aeruginosa. After a brief lag period, multiplication of bacteria was rapid, reaching geometric means of 280,000 after 24 hr and of 5 million after 48 hr. Within 8 hr after inoculation, polymorphonuclear leukocytes (PMNs) began to infiltrate the anterior two thirds of the stroma. Stromal cells adjacent to the injection site became necrotic and appeared to be engulfed by PMNs. By 14 to 16 hr, an abscess containing a dense aggregate of PMNs and multiplying bacteria developed in the central stroma. By 16 to 24 hr, collagen breakdown was apparent within and around the abscess. Ultrastructural evidence of collagen breakdown included loss of intact collagen fibrils, tactoid formation, and accumulation of amorphous electron-dense material. The area of liquefactive necrosis gradually enlarged, and many corneas perforated after 3 to 4 days. Because the course of infection is highly reproducible, this model should prove useful for many studies of experimental Pseudomonas keratitis.