Background: Keratoconjunctivitis sicca (KCS) is a chronic ocular disease of both dogs and humans that can result in ocular discomfort, corneal opacification, and vision loss. Lacritin, a protein found in the tears of many species, has been shown to play a role in lacrimation and corneal health. Because of its role as a potential lacrimostimulant, assessment of endogenous lacritin levels could reveal a correlation between lacritin and tear production in the dog. Objectives: To determine if tear lacritin concentrations are decreased in canine eyes affected by KCS. Animals: 58 client-owned dogs (tear samples from 55 eyes with normal tear production and 55 eyes diagnosed with KCS). Methods: All eyes underwent an ophthalmic exam, including Schirmer Tear Testing (STT), anterior segment assessment, and tear sample collection. Tear samples were evaluated for their total protein concentrations via BCA assay and lacritin concentrations via ELISA. Results: Total protein of canine tears is increased in KCS-affected eyes as compared to normal eyes. Tear lacritin as a component of total tear protein is significantly decreased in tears from KCS-affected eyes. When measured as a concentration (mass per volume of aqueous tears), lacritin is not significantly different between KCS-affected eyes and normal eyes, nor were they strongly correlated to STT values. Conclusions and Clinical Importance: Total tear protein levels were significantly increased in canine KCS. When quantified as a proportion of total tear sample protein, tear lacritin levels are decreased in KCS-affected eyes. Relative to tear volume, tear lacritin levels are not significantly different between KCS-affected eyes and normal eyes. Assessment of lacritin supplementation in canine KCS is warranted to evaluate potential effects on lacrimation and ocular surface health. / Master of Science