A new in vivo method for studying chemotaxis and leucocyte migration was developed in male Wistar rats, using the well characterized chemoattractant, N-formyl-L-methionyl-L-phenylalanine (FMP) as positive control, and dental cotton pellets. 2.0 mg FMP attracted the greatest net leucocytes into test pellets, while doses higher or lower, attracted less cells. Use of L-methionyl-L-leucyl-L-phenylalanine (MLP) as negative control showed that the method could be used to distinguish chemotactic migrations from other migrations. The kinetics of the leucocytic infiltration showed the predominance of polymorphonuclear leucocytes at the early reactions and the arrival of mononuclear leucocytes in later stages. Use of Staphylococcal protein A and trypsin demonstrated that it was possible to assay the activities of those chemoattractants which require complement activation for chemotaxis. However, complement was not normally activated by the technique. The method requires simple surgery, seems a good model for evaluating the in vivo applicability of the numerous in vitro chemotactic findings, and should possibly be used to develop agents such as drugs destined to produce changes in the inflammatory process.