With a view to producing peptides capable of inducing a protective immune response against Schistosoma mansoni and Fasciola hepatica, the sequence and structure of the protective antigens Sm14 and Fh15 were analyzed. Their C-termini showed a high level of sequence conservation which, together with models for their three-dimensional structures, aided in peptide selection. Vaccination trials in Swiss mice challenged with S. mansoni cercaria or F. hepatica metacercaria showed that peptides which included the sequences VTVGDVTA or EKNSESKLTQ were capable of inducing levels of protection equivalent to the recombinant form of Sm14. These peptides may represent an alternative to r-Sm14 for the development of a bivalent anti-helminth vaccine.