The gastrointestinal parasite of dogs and their related species, Toxocara canis, is a prime example of a zoonotic parasite. It is the principal agent of visceral larva migrans and also a cause of ocular larval migrans. As a result of the close association that dogs have with man, the parasite enjoys a world-wide distribution. Infections can be contracted from contaminated soil and handling of infected dogs, and is particularly prevalent amongst professions that have a close association with dogs, such as hydatid control officers in New Zealand. Once inside the non-canid host, the parasite enters a state of arrested development, in which it neither grows nor differentiates. In this state the parasite releases up to 1% of its body weight in excretory/secretory antigens per day. Assuming that this high protein production was in some way linked to immune evasion, a modest EST project was undertaken using a cDNA library generated from infective larvae. The hypothesis behind this approach was that the high protein output demonstrated by these parasites would be mirrored at the mRNA level. In total 266 clones were sequenced, the majority of which were from the both the 5' and 3' ends of the transcripts. Homologues for these genes were sought by similarity searching against the GenBank protein and the dbEST nucleotide databases. Cluster analysis of the clones identified 129 distinct gene products, all but three of which represented new genes. The majority of the genes (96) were represented by single clones, although 8 transcripts were present at high frequencies, each composing >2% of all the clones sequenced. These high abundance transcripts include a mucin and a novel C-type lectin, which together comprise the two major excretory/secretory antigens released by the parasite. Four highly expressed novel transcripts were found, termed ant genes (abundant novel transcripts). Together these genes represented 18% of all the cDNA clones isolated, but no similar sequences occur in the C. elegans genome. While the coding regions of these genes are dissimilar, they exhibit a remarkable level of similarity in their 3' UTR at the nucleotide level. The discovery of these abundant parasite specific genes, of newly-identified lectins and mucins, as well as a range of conserved and novel proteins, provide defined candidates for future analysis of the molecular basis of immune evasion by Toxocara.