Labels and medications with similar appearances have the potential to harm patients and cause delays in hospital services. We report a problem involving the Maxtec MAX-1 and MAX-11 oxygen sensors which are commonly used on anesthesia machines. These oxygen sensors have nearly identical labels which resulted in inadvertent interchanging of the sensors. The incident required the replacement of a MAX-11 sensor with a MAX-1 sensor to ensure proper functioning of the anesthesia machine. Identification of these cases can educate health care professionals of potential sources of labeling errors and safety issues and can also bring about Food and Drug Administration policy changes.