A variety of proteins have been identified in tears, which are composed of secretions from all the orbital glands. It has been assumed that the lacrimal gland was the source of these proteins because there is indirect evidence that the lacrimal gland can secrete protein in response to cholinergic stimulation. In the present study, the concentration of protein was determined in lacrimal gland fluid, i.e., the fluid collected directly from the main excretory duct of the lacrimal gland, uncontaminated by secretions from the other orbital glands. The concentration of protein in the lacrimal gland fluid was higher than that in plasma at lacrimal gland fluid flow rates between 2 and 10 microliter/min, but it was the same as plasma at flow rates slower than 2 microliter/min and faster than 10 microliter/min.