Chronic endobronchial infection frequently caused by gram-negative organisms and an increased, neutrophil-dominated inflammation are characteristics of cystic fibrosis (CF). The present study examines endotoxin levels in bronchoalveolar lavage fluids of CF versus non-CF (N) control children, and correlates these with the inflammatory markers interleukin-8 and neutrophils. Fifty-five patients with CF and 56 patients without CF between the ages of 0.04 to 13.25 years were included. Infection, defined as a bacterial count above 50,000 cfu/ml, was present in 27 CF and 25 N patients. Endotoxin levels were not different between patients with and without CF (infected: 74.9 +/- 12.1 EU/ml versus 51.4 +/- 12.5 EU/ml, p = 0.16; noninfected: 5.9 +/- 4.8 EU/ml versus 11.1 +/- 4.3 EU/ml, p = 0.28). Endotoxin activity correlated to the number of gram-negative organisms in CF and N patients, and endotoxin activity per bacterial colony forming unit did not differ with various gram-negative species. Both interleukin-8 and neutrophils were positively correlated with endotoxin, but this slope was shifted toward higher levels of inflammation in CF patients. We conclude that it is unlikely that higher levels of endotoxin in the absence of viable bacteria explain the increased inflammatory response in CF.