Changes in liver, spleen, kidneys, heart, and brain are reported for Microtus montanus chronically infected with Trypanosoma brucei gambiense. An increase in body weight of infected animals was attributable to a significant increase in total mass of spleen, liver and kidney. Cellular infiltrate consisting primarily of lymphocytes and plasma cells was observed in all organs and was particularly evident in intralobular connective tissue of the liver, adipose tissue of the hilum, and adjacent medullary region of the kidney, spleen, and the meninges. Disruption of normal metabolism and the pathological changes observed in liver and kidney suggest that the survival of trypanosome-infected voles is dependent largely on the physiological response occurring in these organs.