Our objective was to determine the effect of chorioamnionitis on plasma prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) during the first week in preterm infants. Plasma PGE2 and TxB2 were measured at 1, 3, and 7 days of age in preterm infants (birth weights 501 to 1500 g), with ( N = 26) and without ( N = 22) chorioamnionitis. Infants with maternal chorioamnionitis had significantly lower mean gestational age ( P = 0.0001) and birth weight ( P = 0.03) and a marginally higher rate of bronchopulmonary dysplasia (37% versus 12.5, P = 0.05), a result that may be related to the lower mean gestational age. Plasma PGE2 and TxB2 varied widely, more so on the first day but did not significantly differ between the two groups. TxB2 was lower among infants who died or developed morbidities. Circulating PGE2 and TxB2 concentrations in preterm infants in the first week vary considerably, are relatively unaltered by chorioamnionitis, and are lower in association with mortality and clinical morbidities. Further research on their role in the causation of adverse neonatal outcomes is necessary.