Ligaria cuneifolia (R. et P.) Tiegh. (Loranthaceae) (Argentine mistletoe) is usually used in local folk medicine. This work focuses on the hemorrheologic parameters in the treatment with an aqueous extract of Ligaria cuneifolia (Lc) by two different administration routes: intraperitoneal (i.p.) and intravenous (i.v.). Adult male Wistar rats were injected by via i.p. or by via i.v. with: saline solution; 2.5 mg/100 g body weight of Lc and 5.5 mg/100 g body weight of Lc. The relative viscosity of blood (eta r)(45/Hct) was measured showing that Lc-treatment by via i.p. produced an increase of about 69% while Lc by via i.v. enhanced the parameter about 47%. All of Lc-treated animals showed a significant increase in the rigidity index (RI). The mean corpuscular hemoglobin concentration (MCHC) exhibited an increase of about 15% in all the treated groups. Lc-treatment by via i.p. produced a diminution of plasma cholesterol level associated with RI augmentation which induced an increase of (eta r)(45/Hct). By via i.v. Lc produces both RI and (eta r)(45/Hct) augmentation by increasing MCHC but without modifying plasma cholesterol level, indicating a direct Lc-action on the internal viscosity of the erythrocyte.