The limulus amebocyte lysate test has been shown to be a highly sensitive indicator of endotoxin. Our studies showed that as little as 5 ng of endotoxin could be detected in aqueous or vitreous humor in vitro, although 10 microgram endotoxin injected into the aqueous could not be detected. Subsequent studies showed that by diluting the aqueous equally with saline solution, this inhibitory effect could be overcome. Detection of endotoxin elaborated from Pseudomonas aeruginosa was made as early as 24 hours after induced Pseudomonas keratitis or endophthalmitis, whereas staphylococcal-induced keratitis or endophthalmitis gave negative results. Positive cultures using trypticase soy broth or agar slants were observed on all infected animals. Thus, this technique should have ready application for rapid detection of Pseudomonas keratitis or endophthalmitis.