A one-dimensional scanning fluorophotometer (Fluorotron Master) and a two-dimensional scanning fluorophotometer (McLaren and Brubaker) were used to measure rate of aqueous humor flow in normal volunteers. The precision of three protocols of dye application and flow determination was investigated. In all three protocols rate of flow was determined by observing the rate of disappearance of topically-applied fluorescein during an 8-hour period. The three protocols studied were: 1) Two drops of 10% fluorescein washed away five minutes later immediately before beginning measurements of fluorescence. 2) Application of 0.25% fluorescein every 5 minutes for 30 minutes, 6 hours before beginning measurements. 3) Iontophoresis for 7 seconds and irrigation of eye immediately before beginning measurements. Rate of flow was calculated by the methods of Jones and Maurice. The results were compared to measurements made with a slit-lamp fluorophotometer using the technique described by Coakes and Brubaker. The most satisfactory method of measuring flow when either scanning fluorophotometer was employed was to instill fluorescein many hours before measurements begin (protocol 2).