The invention provides excretory/secretory antigens derived from parasitic nematode species which are capable of inducing protective immunity against infection by parasitic nematode species, and related antigenic molecules. The invention also provides nucleotide sequences encoding the antigens and related molecules of the invention, recombinant DNA molecules comprising the nucleotide sequences, and transformed hosts carrying the recombinant DNA molecules. The invention further provides antibodies against the antigens and related molecules, and antibody compositions comprising the antibodies, vaccines comprising the antigens and/or related molecules and methods of treating or preventing nematode infections using the antigens and related molecules, vaccines, antibodies and/or antibody compositions of the invention.