A previous study has demonstrated that 15-deoxy-delta12,14-prostaglandin J2 (15d-PG J2) enhanced acute lung injury induced by lipopolysaccharide (LPS) in mice. The enhancement in acute lung injury by 15d-PG J2 was concomitant with the enhanced expression of interleukin-1beta and chemokines in the lung. However, other underlying mechanisms of this enhancement remain to be elucidated. Cyclooxygenase (COX)-2 has been reported to be involved in enhanced pulmonary permeability during acute lung injury. This study investigated the effects of 15d-PG J2 on COXs expressions in the lung in the presence or absence of LPS. ICR mice were divided into 4 experimental groups that intratracheally received vehicle, lipopolysaccharide (LPS: 125 microg/kg), 15d-PG J2 (1 mg/kg), or 15d-PG J2 + LPS. The expression of mRNA for both COX-1 and -2 in the lung was evaluated 4 h after the intratracheal administration. 15d-PG J2 enhanced the COX-2 mRNA expression in the presence of LPS. In contrast, 15d-PG J2 did not affect the COX-1 expression. These results suggest that the enhancing effects of 15d-PG J2 on LPS-induced acute lung injury might be explained, at least in part, by those on the lung expression of COX-2.