Cystic fibrosis (CT) is associated with chronic lung infection’ inflammation’ and elevated indices of oxidative stress. Recently’ isoprostanes were shown to be a reliable in vivo marker of oxidant injury with 8-iso-PGF2α’ shown to cause airflow obstruction and plasma exudation in guinea pig lung. The present study was designed to examine the relationship between 8-iso-PGF2α levels’ plasma antioxidants’ and clinical status in CF. We hypothesized that plasma 8-iso-PGF2α levels would be higher in subjects with CT compared to healthy controls. Plasma 8-iso-PGF2α levels were prospectively measured in 22 subjects with CF and nine healthy controls using an 8-isoprostane enzyme immunoassay kit along with plasma vitamins A’ E’ and β-carotene. Plasma 8-iso-PGF2α levels were shown to be significantly elevated in the CE subjects compared to controls (319.6±52.6 vs. 145.0±21.0 pg/ml’ P=0.005). Plasma levels of antioxidants were significantly lower for the CF subjects compared to the controls (vitamin A’P<0.003; vitamin E’ P<0.001; and β-carotene’ P<0.01). This study confirns significantly elevated lipid peroxidation in CF using 8-iso-PGF2α levels.