For-Met-delta ZLeu-delta ZPhe-OMe (3) has been synthesized as a new analogue of the prototypical chemotactic agent For-Met-Leu-Phe-OMe (fMLP-OMe). Compound 3 is characterized by presence of two consecutive alpha,beta-didehydro amino acid residues [delta ZLeu = (Z)-alpha,beta-didehydroleucine; delta ZPhe = (Z)-alpha,beta- didehydrophenylalanine] located at the central and C-terminal position, respectively. When tested on human neutrophils the N-formyltripeptide 3, although less active than the parent, is able to induce chemotaxis, superoxide anion production and lysozyme release. The activity of 3 has been compared to that of related fMLP-OMe analogues containing a single delta ZPhe residue located at the C-terminal position.