Progress in the assessment and introduction of new treatments is impeded by the failure to recruit eligible patients into clinical trials. Little is known about the attitudes of U.K. cancer specialists towards trial participation, therefore a postal survey was conducted of 553 British clinical, medical and surgical oncologists. A 45-item questionnaire was returned by 357 clinicians (65% response rate). Although 353 (99%) of respondents stated that they were participating in trials, median 3 (range 0-62), 269 (75%) of clinicians were entering fewer than 50% of eligible patients. Differences were seen between professional groups within oncology; medical oncologists placed more emphasis on research than on clinical activities, felt greater pressure to participate in trials and were more likely to value being known by national and international colleagues than did surgeons or clinical oncologists. Surgeons were more likely to rely on clinical experience rather than enter patients into a trial but were more likely to keep patients on study following relapse. The survey identified constraints imposed by the healthcare system which impede trial participation including lack of time, communication difficulties and conflicts between the role of clinician and scientist. Such factors need consideration when trials are designed. Comparison of British data with those from the U.S. clinicians were broadly similar. The few differences found suggest that the more protocol-driven culture of the U.S. might encourage recruitment and a greater commitment to keep patients on trials.