Influence of citoflavin on dynamics of functional condition of mitogen-induced immunocompetent blood cells at patients with widespread purulent peritonitis is studied. It is established that investigated immunocompetent cells have regulating effect on migration of neutrophil leukocytes at widespread purulent peritonitis during all postoperative period. PHA-activated mononuclear cells don't cause inhibition of migration of neutrophil granulocytes, observed in norm. At the same time the LPS-activated monocytes lead to migration strengthening of neutrophil granulocytes, in comparison with the data received in norm. Usage of citoflavin at patients with widespread purulent peritonitis renders corrective action on immunocompetent cells, changing their properties of regulation of migratory activity of neutrophil granulocytes. It is revealed that such action of citoflavin is connected with function restoration of mononuclear cells to inhibit migration of neutrophil leukocytes and with restoration of stimulation of migration of neutrophil leukocytes under the influence of the LPS-activated monocytes to the values received in norm. The revealed effects at use of citoflavin are most expressed by the 5th day of the postoperative period.