In the present work. we describe the discovery of PW2, a novel peptide presenting in vitro activity against Eimeria acervulina and E. tenella sporozoites. PW2 as selected from phage display (Ph.D.) peptide libraries by an alternative method of panning using living purified E. acervulina sporozoites Lis targets. Our results showed that the peptide disrupts the sporozoite pellicle, resembling the effect caused by most natural antimicrobial peptides, PW2 peptide was also effective against fungi and showed low activity against Toxoplasma gondii tachyzoites, but no activity against Trypanosoma cruzi, Crithidia fasciculata epimastigotes, and bacteria. Additionally, the parasiticidal concentrations of PW2 produced a very low lytic effect on mammalian and avian cells. The effectiveness against Eimeria sporozoites and the absence of adverse effects to host cells indicates that PW2 may be used as a model to generate new drugs for the control of avian coccidiosis. (C) 2002 Elsevier Science B.V. All rights reserved.12015360