This paper summarizes past work detailing the developmental expression, cell and organ localization and biochemical features of the proteins parotid secretory protein (PSP) and isoforms of submandibular gland protein B (SMGB), and describes the molecular characterization of the genes that encode them, Psp and Smgb. These genes appear to be related to the BPI (bactericidal/permeability-increasing protein)/LBP (lipopolysaccharide-binding protein)/PLUNC (palate, lung and nasal epithelial clone) gene family found in the oral and respiratory organs of humans, rodents and cattle. We have emphasized the diverse patterns of expression of these genes among the submandibular, sublingual and parotid salivary glands of the rat, and their potential usefulness in defining and identifying genomic regulatory mechanisms of salivary development. While Psp is expressed similarly in the mouse, the putative Smgb gene of the mouse seems not to be expressed, apparently due to the insertion, between exons 1 and 2, of a gene for a retroviral protein.