Previous attempts to change the prevailing negative attitudes of health professionals toward cancer and cancer patients have consisted mainly of elective courses for small groups of students at advanced levels of medical training. In order to develop more positive attitudes, the Cancer Coordinating Committee at the Medical College of Pennsylvania developed and implemented a required introductory course in oncology for freshman students. The course touched on various aspects of cancer, including epidemiology, prevention, detection, diagnosis, staging, treatment, and rehabilitation. Each session of the course included interviews with cancer patients. Evaluation of the attitudes before and after the course, made with Haley's Cancer Attitude Survey and a Semantic Differential test indicated that on several measures, attitudes toward cancer and cancer patients were more positive after the course than before, and that changes observed were largely maintained over five months. Several attitude changes were not found, in responses related to cancer prevention and detection and the value of early diagnosis. Further changes in the teaching of oncology are suggested: the case for prevention needs to be made more strongly, course objectives need to be clarified, additional materials need to be provided to the students, and the testing procedures should be reevaluated. The required introductory course is recommended not as a substitute for later elective courses, but as an additional part of the curriculum. (MSE)