Babassu is the popular name of Orbignya phalerata Mart. [Arecaceae (Palmae)], which fruits mesocarp has been used in Brazil as medicine for the treatment of pains, constipation, obesity, leukemia, rheumatism, ulcerations, tumors and inflammations. In this study, we investigated the effect of babassu mesocarp flour aqueous extract (BM) on C3H/HePas mice peritoneal cellular migration and macrophage activation by measuring the nitric oxide (NO), hydrogen peroxide (H(2)O(2)) and tumor necrosis factor (TNF) release, spreading activity and major histocompatibility complex (MHC) class II expression. Our results demonstrate that BM injected once ip in mice at 10 and 20 mg/kg increased the cellular influx to the peritoneal cavity, the MHC class II expression and the spreading ability, and also induced the production of NO, TNF and H(2)O(2). The increase in NO-production and MHC expression was also observed after the addition of BM to resident macrophage cultures (100 microg/ml). Thus, BM-treatment was able to activate peritoneal macrophages in vitro and in vivo inducing the production of inflammatory and cytotoxic metabolites, which could justify the popular use of babassu mesocarp in the treatment of tumor diseases, but not in inflammatory pathologies.