BACKGROUND: Platelet-activating factor(PAF) might play an important role in the development of acute respiratory distress syndrome. Since PAF induced lung injury is similar to changes of acute respiratory distress syndrome, and abnormalities in surfactant function have been described in acute respiratory distress syndrome, the authors investigated the effects of PAF on the regulation of surfactant protein A, B and C mRNA accumulation METHOD: The effects of PAF on gene expression of surfactant protein A, B and C in 24 hours after intratracheal injection of PAF in rats. Surfactant protein A, B and C mRNAs were measured by filter hybridization. RESULTS: The accumulation of SP-A mRNA in PAF treated group was significantly decreased by 37.1% and 41.6%, respectively compared to the control group and the group treated with Lyso-PAF(p<0.025, p<0.01). The accumulation of SP-B mRNA in PAF treated group was decreased by 18.7% and 32.2 %, respectively compared to the control group and the group treated with Lyso-PAF but statistically not significant. The accumulation of SP-C mRNA in PAF treated group was significantly decreased by 30.7% and 38.5%, respectively compared to the control group and the group treated with Lyso-PAF(p<0.01, p<0.01). CONCLUSION: These findings represent a marked inhibitory effects of platelet-activating factor on surfactant proteins expression in vivo. This supports, in turn, platelet-activating factor might be related to pathogenesis of acute respiratory distress syndrome.