The heat shock response in selected hydrothermal vent animals was studied. Heat shock protein induction profiles were compiled for three Lau Basin symbiotic mollusks, Induction profiles were used as indices for thermal tolerance and provided physiological data in support of observed species zonation at this site. A new type of thermal gradient block (The High Pressure Thermal Gradient Block) was developed to allow for in vitro investigations of heat shock protein induction in animal tissue at environmentally relevant pressures. The in vitro studies demonstrated protein synthesis is severely compromised in gill tissues from deep dwelling vent mollusks when exposed to 1 atmosphere. The results emphasized the need for performing physiological investigations in deep living organisms at in situ hydrostatic pressures. Heat shock protein induction profiles were obtained by exposing mollusk tissue to a range on incubation temperatures at environmentally relevant pressures in the High Pressure Thermal Gradient Block. The heat shock profiles show all three mollusks to be choosing habitats with temperatures well below their initial HSP 70 threshold induction temperature. The effect of long term environmental temperature on the heat shock response in deep-sea hydrothermal vent and cold seep mussels was also investigated. It was determined that although long term environmental temperatures impact the magnitude and temperature range in which the heat shock response in observed, the heat shock response remains intact in both cold seep and hydrothermal vent mussels examined here. Lastly the effect of hydrostatic pressure on the heat shock response in Bathymodioline mussels was investigated. It was determined that the heat shock response in mussels from depths between 600-900m is not inhibited by changes in hydrostatic pressure. However, inducible heat shock responses in hydrothermal vent mussels adapted to great depths (2500m) only observed in vitro at in situ pressures.