The authors present results of the investigation of melatonin receptors expression in lymphocytes in dynamics in 102 patients with acute pancreatitis of mild and severe form and in 50 volunteers. A correlated analysis was made between obtained results of laboratory and instrumental researches and clinical course of acute pancreatitis. The decrease of MT1 receptors expression was noted on 25% in patients with acute pancreatitis. The decline of MT2 receptors expression was observed on 40% of patients with acute severe pancreatitis and in a case of acute mild pancreatitis — on 15,5%, respectively. Values of MT1 and MT2 expression were equal between healthy volunteers. The decline of MT2 expression was a prognostic unfavourable sign. Obtained results of dynamic expression assessment of MT-receptors were presented as MT2/MT1 indices. Given index didn’t change during disease, because of this, the index could be used as a prognostic development marker of destructive form of acute pancreatitis at the moment of patient’s admission to hospital. Mean values of MT2/MT1 were determined for the purpose of universalization of used method (1,13±0,09 for mild form and 0,81±0,09 for severe form of acute pancreatitis, respectively).