Chronic lung disease (CLD) in preterm infants is due to prolonged inflammation and impaired healing. It has been previously shown thatUreaplasma urealyticum (UU) colonization is associated with CLD(Wang et al, J Pediatr 1995, 127:640-644). We have demonstrated that inflammatory cytokines including interleukin-1β (IL-1β), are increased in lung lavage of infants who develop CLD (J.Interferon and Cytokine Res., in press). We hypothesized that UU colonization in the first week of life induces inflammatory cytokines contributing to the development of CLD. We prospectively obtained endotracheal aspirates or nasopharyngeal washes on day 1 and 7 from 100 infants of BW ≤ 1500gms. IL-1β and IL-1 ra antigen concentrations were measured in tracheal aspirates by ELISA. Fifteen infants were UU culture positive (UU+). UU+ infants were of significantly lower gestational age (25.7±0.4wks, mean±SEM) than UU- infants(28.5±0.3)(p=0.0001). Significant clinical findings were that mothers of UU+ infants had higher incidence of PROM (p=0.003), and received prenatal antibiotics more often (p=0.028). On day 1 there was a trend towards higher IL-1β antigen concentration in UU+ infants (median 47.6 pg/ml, 28.1-92.6, 25th - 75th%tile, n=5) than UU- infants (4.7pg/ml, 0.7-35.1, n=32)(p=0.087). There were no differences in IL-1 ra antigen concentration at d 1 or day 7. These preliminary data suggest that early differences in inflammatory mediators, such as IL-1β may contribute to the development of chronic lung disease in UU+ infants. (Funded by Wyeth-Lederle Neonatology Research Fund.)