The screening of a cDNA library of Taenia crassiceps revealed a clone designated KETc7 that induced high levels of protection against murine cysticercosis in previous experiments. The molecular structure of the deduced 100-amino acid sequence of the corresponding proline-rich polypeptide was studied to detect potentially immunologically active epitopes. Several candidate epitopes were identified, three of which were synthesized by solid-phase peptide synthesis and used as antigens in enzyme-linked immunosorbent assay (ELISA) for detection of specific antibodies in a selected panel of sera from mice infected with Taenia crassiceps and pigs infected with Taenia solium, as well as in the serum and cerebrospinal fluid of human patients with neurocysticercosis. The three peptides detected antibodies in serum from all infected mice. Seven of nine sera from patients with neurocysticercosis reacted strongly with peptide GK-3, and four of them with peptides GK-1 and GK-2. A lower reactivity was observed in sera from experimentally infected pigs. Peptide GK-3 reacted also with 45 out of 77 cerebrospinal fluids (CSF) from patients with confirmed neurocysticercosis and with 14 out of 68 CSF from control patients with other neurological disorders. This is the first report on synthetic peptides that are prominent in the humoral response of murine, porcine and human cysticercosis. Their identification implies finer molecular tools in the exploration of this form of host-parasite relationship, as well as hints to their application in immunodiagnosis and in vaccine design.