The tear-turnover rate of 68 normal human subjects (age range 15-63 yr) was determined using a slit lamp modified to serve as a fluorophotometer. Tear volume and tear secretion, computed from tear-turnover rate, had mean values of 8.47 microliter and 1.78 microliter/min, respectively. Analysis of the results shows a decrease in tear production with age. The mean tear-flow rate was 1.55 microliter/min in subjects aged 15-39 and 0.95 microliter/min in subjects aged 40-63. This fluorophotometer is adaptable to a clinical setting and may prove useful in diagnosis and treatment of anomalies of tear production.