Uncaria guianensis (Aublet) J. F. Gmelin is an herbal medicine from tropical areas of South and Central America. We investigated the anti-inflammatory and anti-allergic properties of an ethanolic extract of U. guianensis leaves, containing alkaloids, flavonoids and phenol carboxylic acids, as revealed by thin layer chromatography (TLC). Oral pre-treatment with U. guianensis inhibited zymosan-induced paw oedema (500 mg/paw) and pleural exudation (100 mg/kg) within 4 h (25-200 mg/kg). U. guianensis (100 mg/kg) inhibited total leukocyte and neutrophil numbers in the pleural cavity 4 h after zymosan stimulation. Pre-treatment with U. guianensis (100 mg/kg, p.o.) inhibited total leukocyte, neutrophil and eosinophil recruitment into the pleural cavity 24 h after LPS (250 ng/cavity, i.t.). Pre-treatment with U. guianensis inhibited paw oedema (25-200 mg/kg) induced by ovalbumin (OVA) within 1 h, and neutrophil and eosinophil recruitment into the mice pleural cavity 24 h after OVA (100 mg/kg). In vitro data revealed that U. guianensis impaired LPS-induced nitric oxide and CXCL8 generation by murine peritoneal macrophages, as well as OVA-induced interleukin-5 synthesis by previously sensitized spleen cells. These results demonstrate that U. guianensis leaves provide effective anti-inflammatory and anti-allergic activities.