Abnormal tear calcium concentrations, which might be expected in ocular and systemic disorders,may be obscured if tear calcium concentration varies with flow rate. The results of the present study indicated that tear calcium concentration is independent of flow rate with rates faster than those which occur with stimulated overflow tearing (i.e., 2 mu1 per minute), but with slower flow rates such as would be encountered with basal, nonstimulated tear flow, tear calcium concentration increases as flow rate decreases. In addition, at given flow rates, tear calcium concentration is the same as that in at least two components of tears, i.e., lacrimal gland fluid, uncontaminated by fluid from the other orbital glands, and fluid from the other orbital glands, uncontaminated by lcarimal gland fluid. It is apparent that only if calcium concentration is correlated with fluid flow rate will determination of calcium in tears and in the components of tears produce valid information not only about tear calcium levels in the presence of ocular and systemic diseases but also about the mechanism of secretion of calcium by the orbital glands.