The rat hst70 gene is specifically expressed in spermatocytes and spermatids. This tissue-specific expression of the gene is primarily mediated through cis-acting elements located within the 0.4 kb segment upstream of the coding region, including two transcription initiation sites. Here, we study the 5' and 3' distal elements flanking the hst70 gene and find that they possess structural motifs characteristic of MAR/SAR elements, and exhibit enhanced affinities for nuclear matrix binding in vitro. Such elements bind efficiently to matrices from either the testis or the liver, i.e. tissues where the gene is either fully active or repressed, although one subfragment in the 5' region was identified as exhibiting testis-specific interactions. Surprisingly, the activity of the CAT reporter gene was repressed in testis-transient transfection assays when the hst70 promoter sequences were extended into the 5' MAR/SAR.