Most primary care physicians are already involved in some form of cancer detection in asymptomatic patients, and most say their involvement is increasing. With the exception of the proctoscopic examination and mammography, major detection procedures are being used with asymptomatic patients by a majority of physicians. In many instances, physicians' use of detection procedures does not conform with guidelines for the cancer-related checkup recommended by the American Cancer Society. Although they may disagree with some guidelines, most physicians agree they are generally helpful. Physicians disagree with guidelines for mammography, because they feel the cost of the test and radiation exposure associated with its use argue against patients' being tested annually, or being tested at all in the absence of symptoms. In contrast, belief that testing is needed at least once a year is the basis for physicians' disagreement with Pap test guidelines. Physicians also resist discontinuing use of the chest x-ray for early cancer detection, because they want to screen smokers annually. While there is substantial agreement on the value of proctoscopy in cancer detection in asymptomatic people, many physicians are not doing a proctoscopic exam if a patient's stool blood test is negative. Patient fear, discomfort, and the cost of testing influence physician decisions against proctoscopic examination. However, the growing interest in flexible sigmoidoscopy may change attitudes and influence practice toward more general use of proctoscopy. Primary care physicians widely support cancer education, both for the public and with patients in their own practice.