Surfactant protein B (SP-B) is an essential component of surfactant that promotes adsorption and spreading of surfactant phospholipids and stabilizes the phospholipid monolayer. SP-B is essential for respiratory function in newborn humans and mice; adult mice with levels of SP-B below 25% of wild type develop fatal respiratory distress syndrome. A potential regulatory function of the C/A(-18) single nucleotide polymorphism in the promoter of the surfactant protein B gene was examined. Transcriptional analysis and ELISA on bronchoalveolar lavage fluid revealed that the presence of the C allele correlated with more SP-B promoter activity and protein. There was approximately 3-fold difference in amounts of SP-B in bronchoalveolar lavage fluid from CA(-18) and AA(-18) individuals. By EMSA, Sp1 bound more tightly to the C allele sequence than to the A allele sequence, perhaps accounting for the differences in transcription. Genotyping of a normal volunteer population showed approximately 31% of the population were AA homozygotes, suggesting that these individuals produce less SP-B. Differences in amounts of SP-B resulting from the promoter SNP could affect the clinical presentation of pulmonary disease.