This study examined dentists' knowledge of infection control, what dentists say they do to control infection, and what procedures they actually take to prevent the transmission of disease. A professional actor, obviously in need of dental care and playing the part of a patient, was sent to three groups of randomly selected dentists in general practice. The dentists were uninformed subjects who were debriefed about the research immediately after their part in the experiment was completed. The study found that dentists apparently know what they should do to protect themselves from contamination. However, very few dentists discussed HIV or AIDS while taking a pretreatment history of a new patient even if that patient was perceived to belong to a high-risk group. The behavior of the dentists indicates a neglect of this important aspect of a thorough history, providing more evidence that emphasis on infection and infection control is necessary in the dental school curriculum and beyond. Unless dentists learn to fully understand what infections their patients may have, they take the chance of transmitting diseases to other patients as well as to themselves, their staff, and their families.