Background: Though mouth-to-mouth resuscitation (MMR) is widely endorsed as a useful lifesaving technique, studies have shown that health care professionals are reluctant to perform it. To characterize the circumstances which facilitate this reluctance among physicians, we have surveyed current and future residency trainees regarding attitudes toward providing ventilation by this method to strangers experiencing arrest in the community. Methods: A total of 280 categorical emergency medicine (EM) and internal medicine (IM) house officers and respective program applicants at a 655 bed Brooklyn, New York teaching hospital were anonymously surveyed regarding their willingness to attempt resuscitation in five hypothetical scenarios of cardiopulmonary arrest. Results: A direct relationship was observed between residency training level and reluctance to perform MMR in each scenario. Applicants expressed greater overall willingness to perform MMR than all residents (56 versus 34%, P<0.00001). Willingness among experienced residents was lower than for junior-level residents (29 versus 40%, P=0.01). EM and IM physicians were statistically indifferent in their responses. There were no differences in willingness to perform MMR by age in MD applicant or resident groups. Conclusions: Many physicians and future doctors are reluctant to perform MMR on arrest victims in the community, a trend that increases in prevalence among those with more residency training. These data support the hypothesis that diminished helping behavior occurs gradually over the training period and may occur as a direct consequence of the training experience. A model for characterizing the elements that make up a rescuer's decision process is proposed.