The recruitment of adequate numbers of people to participate in medical research studies is an ongoing problem for biomedical researchers. Although the general public has come to expect and demand that the biomedical community develop new, safe and effective approaches to the prevention and treatment of diseases, that same public is not aware of the important role that public participation plays in the development of medical advances. Much is known about willingness to participate in research studies from the perspectives of patients, survivors, and those at-risk for getting a particular disease. However, little is known about the attitudes and willingness of the general public to participate in medical research. Yet, it is this population that comprises the potential pool of participants for future treatment and prevention studies. In order to examine public attitudes toward and support for medical research, a random digit dial telephone survey was conducted with 489 persons in southwestern Pennsylvania. The survey measured the respondent's stated willingness to take part in a medical research study and the factors associated with willingness to participate. These included the respondent's health status, demographic characteristics, attitudes and beliefs about participation and their knowledge about the conduct of medical research. The results of the study indicate that 46% of those surveyed said that they would be willing to take part in a medical research study focusing on a new treatment for a specific disease that was of concern to them, 25% stated that they would not be willing and 29% stated that they were undecided regarding participation. However, under certain circumstances, such as having cancer, over half of those who were undecided said they would be willing to participate. The characteristics of those willing to participate in a medical research study differ from those not willing. Determinants of willingness include: having a relative or friend who has an illness, being middle aged (between 35-64 years old), prior experience with participation in a medical research study, having a favorable attitude toward the use of human subjects in medical research and beliefs that diverse types of persons participate in clinical trials. Those respondents who were undecided about joining a clinical trial, also have different characteristics than those who are not willing. The determinants of being undecided in contrast to not willing include: having at least a college degree, having a favorable or neutral attitude toward the use of humans in medical research and, believing that the well-being of participants is the primary concern of researchers. The findings of this study have both public policy and practice implications. From a policy perspective, medical research designed to develop new treatments for disease requires an evidenced-based approach for decision making. Such an approach can only succeed if adequate numbers of individuals are willing to participate in these studies. From a practice perspective, the current study suggests that opportunities exist to increase participation by targeting recruitment efforts not only toward the willing but also toward those who are undecided about participation in medical research studies. This would involve tailoring the content of communications to meet the specific characteristics and concerns of each of these two groups of individuals.