hsp16.6 and its upstream region from the cyanobacterium, Synechocystis sp. PCC 6803, have been analyzed. The hsp16.6 transcriptional start point was positioned 44 base pairs (bp) upstream of the ATG translation start codon. A reporter vector was constructed by ligating the 265 bp upstream fragment onto the upstream region of the lacZ coding sequence. Beta-galactosidase analysis indicated that the 265 bp region did not induce lacZ gene expression in E. coli; although expression was induced when the Synechocystis groESL promoter was used. In Synechocystis cells, lacZ was expressed when the 265 bp fragment was used as a promoter. Cold stress and ethanol did not induce lacZ expression, while heat shock, salt stress, sorbitol, hydrogen peroxide, and high light induced lacZ. A series of deletions from the 265 bp region demonstrated that a region around -35 was essential for hsp16.6 expression.