Antisense oligodeoxynucleotides (ODNs) have been used to effect the specific inhibition of cellular gene expression. We have evaluated the application of this approach to the inhibition of interleukin-1 (IL-1)-induced granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte colony-stimulating factor (G-CSF) expression in cultured human umbilical vein endothelial cells. Antisense ODNs or control ODNs (sense ODNs or missense ODNs containing random base substitutions) were added to cultures of endothelial cells, the cells were induced with IL-1 alpha, and the conditioned media were assayed for GM-CSF and G-CSF by quantitative bioassays and for immunoreactive GM-CSF by enzyme immunoassay. Antisense ODNs complementary to the first 15 or 18 bases of the translation start sites of GM-CSF or G-CSF mRNAs inhibited, in a concentration-dependent fashion, the IL-1-stimulated expression of the corresponding factor, but did not affect expression of the other factor. Control ODNs did not affect GM-CSF or G-CSF expression. Exposure to a GM-CSF antisense ODN, but not a control ODN, substantially reduced cytoplasmic GM-CSF mRNA levels in IL-1-stimulated endothelial cells. Neither ODN affected levels of endothelial leukocyte adhesion molecule (ELAM)1 or glyceraldehyde-3-phosphate dehydrogenase mRNAs. We conclude that antisense ODNs complementary to the translation start sites of GM-CSF or G-CSF mRNAs inhibit expression of the corresponding factor in a sequence-specific fashion and this effect is mediated, at least in part, by reduction in the cytoplasmic level of the targeted mRNA. Moreover, IL-1-induced GM-CSF or G-CSF expression does not depend on expression of the other factor.