Melatonin is a mammalian hormone that has a great variety of effects. At present there is evidence that this hormone considerably reduces the manifestations of many gastrointestinal inflammatory diseases. The biological effects of melatonin are realized through the receptors located on the membranes of different animal cells. Three types of melatonin receptors are now known; of them two (MT1 and MT2) receptors were detected in mammals. Varying clinical forms of gastrointestinal diseases may be pathogenetically caused by the quality and amount of MT1 and MT2 receptors, their ratio, and endogenous melatonin activation. The purpose of this study was to develop a procedure for measuring the human blood cell levels of MT1 and MT2 receptors. For this, specific antibodies to MT1 and MT2 receptors were experimentally obtained; then indirect immunofluorescence was used to determine the content and ratio of blood mononuclear cells having these receptors onto the surface in 23 volunteers. The findings are an initial stage of this study and provide considerable opportunity to study a role of melatonin and its receptors in the pathogenesis of many diseases of the human digestive system.