Most practicing oncologists are committed to the concept of prospective clinical trials but, because of multiple logistic and perceptual deterrents, actually enter only a small portion of their patients into such studies. Physician concerns include discomfort with placebo or "no treatment" randomizations, the burden of cumbersome monitoring of protocol patients, and fear of displeasing referring physicians. Patients have difficulty accepting the uncertainty of randomized trials, particularly those with a placebo arm. They resent the inconvenience and expense of extra visits and studies associated with protocol participation. Informed consent documents are often complex and their intent misconstrued by patients. Rigorous eligibility requirements, although necessary for accurate analysis, reduce accrual. Multiplicity of protocols, with the resulting necessity to prioritize, rapid closure of Phase II studies for common tumors, and negative public attitudes reinforced by the media are significant deterrents to clinical trial participation. Increasing accrual is a daunting challenge to the physician. Simplification of burdensome data collection, consent forms, and institutional review board procedures will reduce reluctance to participate. Most important, physicians must be educators, emphasizing the advantages of clinical trials to their patients and their families, their colleagues, and the public.