Marine mammals are known to dive up to 2000 m and, therefore, tolerate as much as 200 atm. of hydrostatic pressure. To examine possible metabolic adaptations to these elevated pressures, fresh blood samples from marine and terrestrial mammals were incubated for 2 h at 37 degrees C under 136 atm (2000 psi) of hydrostatic pressure. The consumption of plasma glucose and the production of lactate over the 2-h period were used to assess glycolytic flux in the red cells. The results indicate that glycolytic flux as measured by lactate production under pressure can be significantly depressed in most terrestrial mammals and either not altered or accelerated in marine mammals. The data also suggest that there is a significant shift in the ratio of lactate produced to glucose consumed under pressure. Interestingly, human and dolphin blood do not react to pressure. These combined data imply a metabolic adaptation to pressure in marine mammal RBC that may not be necessary in human or dolphin cells due to their unique patterns of glucose metabolism.