Oxygen uptake, CO2 elimination, blood gas tensions and pH of the hydrated, 24 hrs water-deprived and aestivated toad, Bufo marinus were measured, and plasma samples from same specimens were assayed on the vas deferens of mice for opiate activity. Following 24 hrs of water deprivation, oxygen uptake decreased by 22%, CO2 elimination and oxygen tensions of blood were slightly feduced, and plasma opiate activity remained unaltered. Aestivation resulted in an increaseof plasma opiate activity to 225% of the con...