We characterize a cluster of three genes, named Mst57Da, Mst57Db and Mst57Dc, according to their localization at polytene band 57D and their selective expression in Drosophila melanogaster males. Within a 4 kb segment of genomic DNA these genes code for poly(A)+ RNAs of about 750 nt, 650 nt and 850 nt length that are restricted to the male accessory glands. They all contain relatively long 5' and 3' untranslated regions compared to the size of their open reading frames. The 5' untranslated regions are characterized by several short open reading frames. In addition, the genes Mst57Da and Mst57Db share a 14 nucleotides long conserved sequence block in front of the putative translated regions. We propose that these common features are structural elements important for translational control of these genes. The predicted sequences of the small proteins of 55, 40 and 42 amino acids suggest that two of them (MST57Da and MST57Db) are secretory proteins and therefore components of the paragonial secretions. In P-element mediated germ line transformations of Mst57Db/lacZ fusion genes, a short gene fragment of -187/+395 is still specifically expressed in the paragonia. In addition, regions involved in negative and positive control of transcription have been identified. Development of a supernumerary paragonial gland is frequently observed in transgenic, intersexual genotypes indicating that in intersexes cells derived from the female genital disc can develop male genital structures.