Studies of the clinical value of the limulus amebocyte lysate test for the detection of endotoxemia are inconsistent. In an attempt to define the value of this test, a total of 237 plasma samples from 111 patients were tested for endotoxin with seven different lysate preparations. A total of 48 plasma samples yielded a positive test with one or more of the seven preparations. Two of eight samples positive with all seven preparations were from ambulatory patients. A significant positive correlation of the test with bacteremia, neutrophilia and elevated serum alkaline phosphatase was found. Only three of the 48 positive tests occurred by four hours of incubation, and only 12 were associated with positive blood cultures (eight contained gram-negative bacteria). The test now available has no clinical usefulness in the detection of endotoxemia or gram-negative septicemia.