Fluids from the KTB pilot hole were examined for the presence of possibly existing hyperthermophiiic microorganisms. Due to the expected low cell concentrations in the fluids, all particles (including organisms) were concentrated about a factor of 10000 by ccntrifugation. From these samples, enrichments of hypcrthermophiles were attempted at incubation temperatures
between 85 and 120 °C at low (300 kPa) and high (25000 kPa) pressure. However, no hyperthermophilic microorganisms could be enriched from the concentrated samples.