An abundant 1.05 kb human lacrimal gland mRNA has been characterized by cDNA cloning. It encodes a predicted 180 residue, 20546 Da secreted protein, with a charge of +11 at pH 7 and 24.5% proline, designated as Basic Proline-rich Lacrimal Protein (BPLP). Southern blot analysis is consistent with a singleBPLPgene. BPLP lacks any distinct repetitive structure, and is unrelated to the salivary proline-rich protein super-family. The pre-proprotein shows modest overall similarity to a superfamily comprising human PRPb, the mouse MSG proteins, and rat VCS-αl, VCS-β1 and submandibular apomucin. BPLP also contains a domain with similarity to the Zp2 protein domain found in several otherwise unrelated proteins. Northern blot analysis indicated that theBPLPgene is also expressed at modest levels in the human submandibular gland, andin situhybridization demonstrated expression ofBPLPin the secretory end-pieces of the human lacrimal gland. TheBPLPcDNA clone defines a new human tear protein, and should provide a useful phenotypic marker of differentiation inin vitrostudies of lacrimal gland function.