Minced polyester threads introduced into peritoneal cavity of guinea pigs or rats cause a granulomatous inflammation with evidence of macrophage stimulation. Chemotactic agents play an important role in the inflammatory reaction; they may be exogenous and/or endogenous. These are released locally by the cells involved in inflammation. In this paper the chemotactic effects of the peritoneal fluids from rats bearing the polyester inflammatory process, have been studied on PMN cells "in vitro". The peritoneal cavity fluids were obtained by washing the cavity of untreated rats or rats intraperitoneally injected with polyester, 1, 3, 7, 14 days after the intraperitoneal injection. The chemotactic response was assayed by employing modified chemotaxis Boyden chambers (Blind Well Neuro Probe) and polymorphonuclear leukocytes from normal or treated rats. Quantification of the migration was calculated by chemotactic index (A/B) (B = random migration, A = chemotaxis). The results demonstrated that the peritoneal fluids taken 3 and 7 days after the intraperitoneal polyester injection, elicit an evident chemotaxis response greater than that showed by peritoneal fluids from control rats. It is suggested that chemotactic factors can be produced and released by mononuclear cells involved in the inflammatory process.