Histopathological findings on brain, heart, liver, and spleen of albino rats and white mice, infected with different stocks of Trypanosoma brucei gambiense of human origin are presented. Classical brain lesions, including chronic inflammation of the choroid plexuses, were observed in all infected animals, the severity of which increased with the chronicity of the disease. Parasite stocks which gave rise to a less acute course of the disease more often induced myocarditis, while brain lesions were less pronounced, suggesting that virulence of the parasites is more closely related to the advent of myocarditis than to the appearance of brain lesions. Liver lesions were not obvious. In spleens, a variable and often very pronounced degree of lymphoid hyperplasia was observed.