Growth and transcriptional profiles of the deep-sea methanarchaeon Methanocaldococcus jannaschii were studied under sudden up-shifts of temperature and pressure. Application of 500 atm of hyperbaric pressure shifted the optimal growth temperature upwards by about 5 degrees C in a high temperature-pressure bioreactor, and increased the specific growth rate threefold at 88 degrees C. In contrast, pressure-shock from 7.8 to 500 atm over 15 min, the first such pressure up-shift reported for a piezophile, did not accelerate growth. High-pressure heat-shock from 88 to 98 degrees C, a condition relevant to the turbulent in situ surroundings of deep-sea hydrothermal vents, resulted in termination of growth. Transcriptional profiles for cells grown at 88 degrees C and 500 atm, heat-shocked at 500 atm, and pressure-shocked to 500 atm, shared a subset of genes whose differential expression was attributed to elevated pressure. In the pressure-shock case, this transcriptional response was evident despite the absence of a piezophilic growth response. In all, despite the piezophilic capacity and high-pressure origins of M. jannaschii, the core pressure response was remarkably limited and consisted of differential expression of genes encoding three hypothetical proteins and a gene involved in DNA recombination.