Cathartes aura is a bird used in the Mexican traditional medicine for the empirical treatment of cancer, injuries, infections and burns.The in vitro immunomodulatory effects of Cathartes aura extract (CAE) were evaluated estimating its effects on proliferation of human peripheral blood mononuclear cells and murine splenocytes. The effects of CAE (1–200μg/ml) on NO production, pinocytosis and lysosomal enzyme activity were assayed in murine macrophages RAW 264.7. The cytotoxic effects of CAE (1–500μg/ml) on tumorigenic and non tumorigenic cells were evaluated using the MTT assay.In the absence of LPS, CAE induced the proliferation of murine splenocytes (119%), enhanced the pinocytosis (113%) and lysosomal enzyme activity (141%) in murine macrophages with a similar potency than lypopolisaccharides 1μg/ml. In addition, CAE exerted cytotoxic effects mainly on human cervical cancer cells (IC 50 =117μg/ml) but lacked toxic effects on non tumorigenic cells (IC 50 >500μg/ml).Cathartes aura exerts immunostimulatory and cytotoxic activities