The ?ZAP II expressed genomic library of B. pseudomallei was screened with pooled melioidosis serum preabsorbed with E. coli host cell. The positive clones were detected by using protein A-CDP-star chemiluminescence. All of 14 positive clones reacted with only the pooled absorbed melioidosis serum and not the pooled absorbed normal serum when tested with the plaque dot blot analysis. The expressed genes were detected by using a combination of immunoscreening, bioinforrnatics and molecular biology. At least six in viva expressed genes were identified by this approach. Two were well known virulent genes, gmhA (a capsule biosynthetic gene) and bipD (type III secretion protein gene). Another two were genes coded for conserved hypothetical protein. The last two isolated genes were groEL (a chaperonine protein gene), and a gene encoding transmembrane protein.