We have shown previously that lung surfactant inhibits nitric oxide production at the post-transcriptional level in lipopolysaccharide(LPS)-stimulated rat alveolar macrophages (Miles et al., Am.J.Physiol. 276:Ll86, 1999). In this study, we examined the effect of lung surfactant (200 microg phospholipid/ml), isolated from rat lung lavage, on the production of two pro-inflammatory cytokines, IL-1B and TNF-a, by LPS-stimulated rat alveolar macrophages. After 22 h incubation with LPS plus lung surfactant, IL-1B and TNF-a production was reduced by 77% and 95%, respectively. mRNA levels were measured by Northern blot analysis, performed 4 hours after LPS-stimulation using digoxigenin-labeled probes. There was no difference in IL-1B or TNF-a mRNA levels between cells stimulated with LPS with or without lung surfactant. Nitric oxide, IL-1B and TNF-a are known to be regulated at both the transcriptional and post-transcriptional levels. It is interesting that lung surfactant inhibits the production of all three pro-inflammatory molecules at the post-transcriptional level. This suggests that the post-transcriptional regulation of these three molecules may share a similar mechanism.