The process of recruitment and screening of volunteers for clinical research studies has not been thoroughly evaluated in the ophthalmic literature. The data for the current report were derived from a double-masked randomized clinical trial designed to evaluate and compare the effective tear level concentrations of three topical ophthalmic medications. Subjects were recruited from the general population and were healthy volunteers on no medications. Tear volume was measured by the Schirmer test with anesthesia; acceptable results were in the range of 10-25 mm/5 min. Study enrollment was limited to 32 subjects per week, with a total sample size goal of 320. The study population, 18-45 years of age, consisted primarily of white male college students. Nine hundred fiftyseven volunteers were recruited. Of the 498 of these subjects that reported for screening (52%), 459 (48%) were actually screened, and 320 (33%) were enrolled. The overall prevalence of an abnormal Schirmer test (<10 or >25 mm/5 min in either eye) in the screened population was 22%. The frequency of decreased tear production (13%) was slightly greater than that of increased tear production (9%). An abnormal Schirmer test was the primary reason for ineligibility. The completion rate for those enrolled was 96%. This type of information is valuable when designing a clinical trial, especially with regard to budgetary, time table, and sample size estimations.