Laboratory tear function tests, such as the lactoferrin and the lysozyme test, reflect the level of tear gland deficiency and are, therefore, very useful for the clinician in the diagnosis of keratoconjunctivitis sicca (KCS). Although these tests do have an excellent discriminatory ability, they should be used in addition to clinical tests, such as the Schirmer-1 test, the tear film break-up time (BUT) and the Rose bengal (Rb) staining test. Schirmer's test, the most commonly used clinical test, measures tear fluid production. The tear film BUT, on the other hand, is the only test which establishes tear film instability. The Rose bengal score is strongly related to secondary damage of the superficial epithelium of the cornea and conjunctiva in patients with KCS. Thus, combining the results of these various tests facilitates the diagnosis of KCS and also the differentiation between Sjögren's KCS and non-Sjögren's KCS.