Five hundred forty-seven reports of adverse reactions to timolol maleate received by the National Registry for Drug-induced Ocular Side Effects during an eleven-month period were reviewed. Approximately half the reports concerned systemic reactions affecting the cardiac, pulmonary, central nervous, gastrointestinal, and dermatologic systems. Most serious were depression, anxiety, and confusion; bradycardia and arrhythmias; and pulmonary airway obstruction. Half of the ocular side effects concerned external ocular disease, of which superficial punctate keratitis and corneal anesthesia were the most remarkable. Ten percent of the reports described a visual disturbance which, in many cases, was not associated with refractive error.