Another approach for the identification of genes that code for antigenic products is described using an antigenic sequence tag (AST) strategy. A Schistosoma mansoni adult worm cDNA library was screened with affinity chromatography-purified immunoglobulins from infected human sera and a mild oxidation treatment with sodium periodate. From 1 or both ends of 30 cDNA clones, 30 ASTs were obtained. Of these, 22 were previously known Sm antigens. One clone had matches with entries for other organisms in the databases and 6 had homology with Sm-expressed sequence tags (EST) entries. These clones, together with another 1 that had no significant database matches, were considered new antigenic genes in S. mansoni. The strategy proved to be efficient for the identification of genes that could be used for immunological studies and evaluation as vaccine candidates.