In the present study, a genomic DNA clone encoding the medfly homolog of Drosophila melanogaster hsp27 gene, named Cchsp27, was isolated. We sequenced a part of the clone containing the coding region, the 5' untranslated region and approximately 2.8 Kb of the 5' flanking region of the gene. Phylogenetic analysis of several insect small heat shock proteins, suggested that CcHsp27 is orthologous to Drosophila Hsp27 and Sarcophaga crassipalpis Hsp25. The Cchsp27 gene was mapped at the 81A division of the sixth chromosome which coincides with one of the major heat shock puffs of medfly. Structural analysis of the 5' flanking region of the Cchsp27 gene revealed the presence of five putative heat shock elements and one putative ecdysone response element. In addition to heat induction, the Cchsp27 gene was expressed at several stages of normal medfly development. In general, the developmental expression pattern of the Cchsp27 gene was similar to the respective pattern of Drosophila hsp27 gene. However, there were some important differences in certain developmental stages suggesting differential regulation of the hsp27 gene in the two dipterans species. Salivary gland culture experiments showed that the Cchsp27 gene is regulated by 20-hydroxyecdysone.