High hydrostatic pressure (HP) increases Hsp70 protein and mRNA levels by increasing the mRNA half-life without activation of HSF1 transcription factor. We investigated whether this change in gene expression requires Hsp90, previously shown to regulate hsp70 genes via HSF1. In HeLa cells, both HP and Hsp90 inhibitor geldanamycin (GA) up-regulated Hsp70 expression through mRNA stabilisation. GA, unlike HP, increased HSF1 activation. However, when exposures were used together a marked Hsp70 response was observed with mRNA stabilisation without coincidence of HSF1 activation. Our data suggests that Hsp90 is involved in hsp70 mRNA stabilisation and the HSF1 activation can be suppressed by high HP.