Investigations of the normal osmolar relationship between aqueous and plasma have demonstrated an aqueous osmolar excess in several mammalian species.8,17,24,25 This excess is considered to be the dominant driving force in aqueous humor formation.1,16,19 As acetazolamide significantly decreases the aqueous flow rate,4-6,21 an alteration in the aqueous-to-plasma osmolar relationship might reasonably be expected following the administration of the drug. Urrets-Zavalia and Remedi27 have demonstrated a lowering of the osmolar concentration in the dog aqueous following administration of acetazolamide, on the basis of alterations in electrical conductivity. However, no associated plasma values are reported. The present investigation has been undertaken as a further study of the aqueous-to-plasma osmolar relationship. Method Adult male albino rabbits weighing from 2.5 to 3.5 kg. were utilized, and each eye was used only once for aqueous puncture. They were allowed food (Wayne Rabbit Pellets) and water without restriction. Twenty-four hours before use