Swiss-Webster mice challenged intracorneally with varying doses of Pseudomonas aeruginosa exhibit eye infection within 24 h as detected by corneal opacity. The infection remains localized and spontaneously heals within 4-6 wk. However, when mice are pretreated with a single i.p. injection of cyclophosphamide 4 days prior to intracorneal or anterior-chamber challenge with various bacterial cell suspensions (10-108), 83% of the anterior chamber and 54% of the intracorneally challenged mice (most at higher dilutions of the bacteria) died of Pseudomonas septicemia within 48 h. Corneal damage was histochemically and ultrastructurally observed in surviving animals by 24-48 h following challenge by either route.