Early clinical studies revealed that timolol and other topical β blockers were effective in reducing intra‐ocular pressure, without the side effects associated with other antiglaucoma agents. However, because persons with cardiovascular or respiratory diseases were generally excluded from many of these early studies, the risk of serious cardiovascular and respiratory side effects was seriously underestimated. Once these drugs were made available to the general population, reports of systemic side effects began to proliferate. Very quickly, adverse effects from topical β blockade became “old news.” Despite this recognition, many treating physicians remained unaware of the potential for systemic β blockade from topically applied β blockers. A significant portion of a topically administered dose of a β blocker can be absorbed and thereby affect systemic β blockade. Sensitivity to systemic β blockade can be quite dramatic in certain highly susceptible patients, particularly those with either cardiac or pulmonary abnormalities. Careful review of patients' medications will generally lessen, but not completely eliminate, the risk of undesired complications attributable to topical P blockade.