A gene coding for the 30 kDa Schistosoma mansoni cercarial protease was amplified using the polymerase chain reaction (PCR) from genomic DNA templates. Cloning and sequencing of several independent PCR clones revealed the presence of an intron additional to the one described in the original cloning of the gene. The 3 exons were cloned into expression vectors so that they could be expressed as separate glutathione-S-transferase (GST) translational fusions. Recombinant bacteria carrying these expression plasmids expressed the fusion proteins at high levels. Western blotting of bacterial lysates with sera raised against the native S. mansoni cercarial protease showed that all 3 exons were recognized. Thus we have produced recombinant bacteria capable of providing large amounts of an S. mansoni antigen for immunological studies and evaluation as a candidate vaccine.