The complex molecular systems involved in the process of sex-differentiation and fertility in Schistosoma mansoni have not yet been completely described. Using a 4608-element cDNA microarray, we have now determined 90 and 139 genes with significantly (q-value</=0.06) higher expression levels in adult males and females, respectively. Eight out of eleven (73%) selected transcripts had their differential expression levels validated by real-time RT-PCR. One of these transcripts was extended by RT-PCR and was shown to span the intronic region between exons 9 and 11 of the S. mansoni CA150 gene, a transcriptional cofactor known in humans to interact with both RNA polymerase II and the spliceosome complex. The longer transcript probably represents a novel isoform of S. mansoni CA150. Additionally, we obtained full-length sequences for three other isoforms of the SmCA150 gene, coding for proteins of different lengths and domain compositions. Semi-quantitative RT-PCR showed different expression ratios among these isoforms between male and female. Due to the role of CA150 in RNA transcription and processing, we hypothesize that these differential expression events may be important in the generation and maintenance of the different phenotypes between male and female.