Previous studies evaluated the prudent use and potential over use of drug screens in clinical decision making. However, the percentage of emergency physicians who can correctly identify which drugs are found on their hospital's basic drug screens has not been established. Results of physician closed-ended questionnaires were compared to the results of a telephone survey with each physician's individual hospital laboratory. Eighty-one (35.7%) of 227 emergency physicians responded. Four (4.9%) correctly identified what was on their individual institution's urine drug screens and 17 (21%) correctly identified what was on serum screens. In other results, 74.3% erroneously relayed that all benzodiazepines can be found on urine drug screens and 46.3% incorrectly answered that acetaminophen would be found on basic quantitative serum screens. Drug screen results can be misinterpreted if the drugs the physician expects to be screened for, and what is actually screened for, are not the same. Pharmacy and laboratory personnel have a responsibility to keep the physician informed of drug screen issues. They should be proactive in advising physicians of changes in drug testing and new drug screening methods or by providing reports on the occurrence of false positive results.