To determine if compliance with timolol treatment was better than compliance with pilocarpine treatment (as reported previously), we measured compliance with timolol treatment in a sample of 110 patients using an unobtrusive eyedrop medication monitor, which recorded electronically the date and time of each drug administration over a four- to six-week period. The patients administered a mean ± S.D. of 82.7% ± 19.0% of the prescribed timolol doses (range, 20% to 100%). Forty-five patients were treated concurrently with timolol and pilocarpine. These patients administered a mean ± S.D. of 84.3% ± 14.0% of the prescribed pilocarpine doses (P=.012, and van der Waerden test). Our results suggest that while compliance is influenced by the drug regimen, defaulting is not eliminated by prescribing a more convenient medication with fewer side effects.