BACKGROUND: Our goal was to examine the following issues relevant to the use of liquid medications: (1) which liquid medication dosing devices are commonly owned and used; (2) the ability of potential patients to accurately measure liquids using 3 different dosing devices; (3) their ability to correctly interpret a variety of dosing instructions; and (4) their ability to correctly interpret a pediatric dosing chart. METHODS: One hundred thirty volunteers from the waiting areas of 3 primary care clinics in the St. Paul, Minnesota, area were interviewed. Participants were shown 7 liquid dosing devices and were asked which they had in their homes and which they had ever used. The participants were tested and scored on their ability to measure liquid medicines and interpret dosing instructions accurately. The total performance score was determined, with a maximum obtainable score of 11. RESULTS: A household teaspoon was the device most frequently used for measuring liquid medication. Women and participants with more education had higher total performance scores. Common errors included misinterpreting instructions, confusing teaspoons and tablespoons on a medicine cup, and misreading a dosage chart when weight and age were discordant. CONCLUSIONS: Clinicians need to be aware that many people continue to use inaccurate devices for measuring liquid medication, such as household spoons. They should encourage the use of more accurate devices, particularly the oral dosing syringe. Clinicians should always consider the possibility of a medication dosing error when faced with an apparent treatment failure.