Using an unobtrusive eyedrop medication monitor, we measured compliance with topical pilocarpine treatment in a sample of 184 patients. The eyedrop monitor recorded electronically the date and time of each pilocarpine administration over a four- to six-week period. The subjects administered a mean ± S.D. of 76.0% ± 24.3% of the prescribed pilocarpine doses. Eleven patients (6%) took less than one quarter and 28 patients (15.2%) took less than one half of the prescribed administrations. In contrast, when the subjects were interviewed they reported taking a mean ± S.D. of 97.1% ± 5.9% of the prescribed pilocarpine doses. As determined by the monitor, 45 patients (24.5%) had at least one day per month with no administrations of pilocarpine; 56 subjects (30.4%) compressed the doses during the daytime hours, leaving an interval between the night dose and the morning dose the next day of 12 hours or more. The rate of compliance was significantly higher (P<.0001) in the 24-hour period preceding the return appointment than in the entire observation period.