Major recent advances in deep-sea biotechnology have come in the form of continuing discoveries of novel microorganisms, unexpected genetic diversity, and new natural products of potential relevance to human health or environmental bioremediation. Continuing explorations of submarine hydrothermal vent environments have yielded new hyperthermophiles (maximal growth at 90 degreesC or greater) and more evidence that elevated hydrostatic pressure stabilizes cells and enzymes at high temperature. Vent samples have also yielded new mesophiles (optimal growth near 30 degreesC) that produce heparin-like exopolysaccharides or express extraordinary tolerance (removal by precipitation) of heavy metals. From the cold deep sea have come new findings of unexpected microbial diversity and the promise of industrially useful enzymes or secondary metabolites. New classes of predictive models are emerging to guide future exploration of microbial diversity in the deep ocean.