The nematode Toxocara canis is a cosmopolitan parasite of canids with a broadparatenic host range that includes humans.We generated two libraries from male and female adultT.canis,and analyzed the expressed sequence tags(ESTs)to identify genes involved in sexualdetermination,reproduction,and development.A total of 4328 clones were sequenced,yielding3803 ESTs with an average sequence length of 688 bp.The cluster and assembly analysis yielded1027 unique sequences that included 323 contigs and 704 singletons.BLASTX searches revealed384 unigenes that had no significant matches to published sequences,which comprised 37.39%ofthe total number of sequences.The remaining 643 unigenes(62.61%)shared high levels ofsequence identity with published nucleotide or amino-acid sequences.Based on overall ESTabundance,the major sex-related genes were major sperm protein isoform beta(329,13.57%)andimmunosuppressive ovarian message protein(45,3.27%).Through comparisons with data fromprevious studies,33 sex-related genes were identified,which comprised 3.21%of the total uniquecDNAs.The transcription profiles of ten of these sex-related gene homologs were examined inmale and female adult T.canis using reverse transcription and real-time polymerase chain reaction.Our findings will aid future investigations of sex-related gene expression in T.canis,and provideinsight into novel molecular targets for the control of the parasite.