The rate of aqueous formation was measured with fluorophotometry in a group of 113 normal human subjects who ranged in age from 20 to 83 years. A slight decrease in the rate of aqueous humor formation with aging was detected, but the rate was remarkably stable. The rate of aqueous humor formation was more stable than intraocular pressure or anterior chamber volume in this group and more stable than the tonographic C value reported by other investigators.