Epidermal growth factor (EGF) stimulates surfactant protein A (SP-A) synthesis in human fetal lung explants through ligand binding to the EGF receptor (EGF-R). We hypothesized that inhibition of EGF-R mRNA would block surfactant protein A expression in spontaneously differentiating cultured human fetal lung tissue. Midtrimester human fetal lung explants were maintained in serum-free Waymouth's medium for 3 days. The explants were exposed to an antisense 18-mer phosphorothioate oligodeoxynucleotide (ODN) targeted to the initiation codon region of EGF-R mRNA at a concentration of 90μM. A sense ODN similarly modified was used as an additional control. Lipofectamine was used as a carrier, and the medium was changed daily with fresh ODN added. Due to the low abundance of EGF-R mRNA transcripts, the level of EGF-R mRNA was semi-quantitatively determined by reverse transcriptase polymerase chain reaction (RT-PCR). We found a significant 3-fold decrease in EGF-R mRNA levels in the antisense treated groups compared to control, with no effect seen in either the sense or vehicle conditions (ANOVA, n=7, p<0.001, Newman-Keuls p< 0.05 for antisense ODN compared to the other conditions). SP-A mRNA levels were measured by Northern blot analysis under the same conditions as described above. The densitometric data from the Northern blots were normalized to β-actin to control for loading. Treatment with antisense EGF-R ODN decreased SP-A mRNA levels by 4-fold compared to control, with no effect seen in either the sense or vehicle conditions (ANOVA, n=5, p< 0.01, Newman-Keuls p<0.05 for antisense ODN compared to the other conditions). The ODNs did not affect tissue viability as measured by the release of lactate dehydrogenase into the media. We conclude that selective degradation of EGF-R mRNA with antisense ODNs results in a decrease in SP-A gene expression in human fetal lung. We speculate that the EGF receptor pathway plays an important role in the regulation of SP-A during human fetal lung development.