The tear fluid contains proteins which are synthesized locally in the conjunctiva and lacrimal glands, and others, which reach the tear fluid from the blood circulation. It is generally accepted that serum albumin (HSA) belongs to the latter group of tear proteins. Consequently, the ratio between the levels of HSA in the tear fluid and in the blood serum can be used as a parameter for the degree of vascular leakage. All blood-borne tear proteins will show concentration ratios in tears and blood serum similar to HSA, provided that they pass through the blood-tear barrier at the same flow rate as HSA. This principle may be used to determine whether a certain tear protein is blood-borne or locally synthesized. An additional method to determine the source of tear proteins is supposed, and is based on the assumption that blood-borne proteins will occur in tears from both eyes at a concentration ratio similar to that of HSA, whereas the concentration ratios of locally synthesized proteins will not be related to the HSA-levels in the tears of the two eyes. This method is independent of the rate of diffusion through tissue barriers. In the present study these methods have given coordinating and supplementary information. The IgG and IgM contents of tears from healthy eyes and from patients with vernal keratoconjunctivitis (VC) were shown to be essentially blood-borne. In tears from VC-patients as well as from healthy controls, IgE was usually found to be a product of local synthesis. In tears from healthy eyes, IgA was almost entirely synthesized locally, but a significant part of the IgA in tears from inflamed eyes was blood-borne. The geometrical mean (GM) of blood levels of IgE for VC-patients was not increased in relation to the GM for healthy controls of the same age groups. In contrast, the GM for IgE in tears from VC-patients (27.5 I.U./ml) was higher than the GM + 2 SD for the healthy controls (4.1 I.U./ml) and also than the highest level of IgE observed in tears from healthy eyes (6.6 I.U./ml). The tear-levels of IgE for VC-patients were strikingly dynamic and in some patients a hundred-fold increase or decrease was observed in the course of a relatively short time period. In contrast, alterations of blood-levels of IgE and of tear levels of IgA were relatively moderate. These results indicate a marked association between VC and an increased IgE-content of tears derived from local immunocytes. However, in some patients apparently suffering from typical VC, normal IgE-levels were consistently found in tears from both eyes during a number of relapses or aggravations of the disease. These results may indicate that more than one etiopathogenesis may lead to the clinical condition known as VC. A hitherto unexplained feature of VC is the pronounced lacrimation. We have shown that the concentration of the essential tear-proteins is not decreased in VC. Lacrimation is therefore associated with accelerated protein synthesis of the secretory system.