Aqueous flow in normal human eyes was assessed at 1 hr intervals via fluorophotometric measurements, starting 4 hr after fluorescein instillation. The average coefficients of variation of the individual flow values were 5.3% and 8.4% for 1 hr and 1 week intervals, respectively. Aqueous flow was measured in 11 healthy volunteers after the instillation of phenylephrine. In the first hour the aqueous flow showed a significant increase: 131% +/- 72% (P less than 0.001) and in the second hour: 121% +/- 92% (P less than 0.002). Between 2 and 5 hr the average flow did not differ significantly from the flow in the untreated fellow eye. There was no marked effect of pupil dilation on aqueous flow.