In a feasibility study of mass population screening for breast cancer by clinical examination and mammography the ability of non-medical staff (nurses and radiographers) to act as primary screeners was compared with that of medical staff (surgeons and radiologists). In 240 women with cancer the rate of detection of the disease by the non-medical staff was comparable to that of the medical staff, although the non-medical staff detected more cancers by mammography alone than did the medical staff. The rate of detection by surgeons and particularly nurses was lower in women without symptoms than in those with symptoms, whereas the incidence of detection by radiologists and radiographers was lower in women aged under 50 than in those over 50. The rate of detection by all groups of staff significantly increased with increases in tumour size. The results suggest that non-medical staff can act effectively as primary screeners, but that for the detection of cancer in asymptomatic women, particularly those over 50, mammography is probably more effective than clinical examination.