Screening for breast cancer using the combination of physical examination of the breasts and mammography was effective in women age 50 or more in the HIP study. However, major questions remain, especially the benefit of screening women age 40-49, and the independent effect of mammography. Such questions can only be answered by large-scale randomized controlled trials, and trials to answer these questions are now underway in Canada (the NBSS) and Sweden. Only the NBSS, however, is attempting to replicate the HIP study in women age 40-49, and to evaluate the additional contribution of mammography to annual physical examination in women age 50-59. The Swedish studies are evaluating the effectiveness of mammography alone, while studies in Britain will help to evaluate breast self-examination (BSE) and biannual mammography with annual physical examination. Because much of the benefit in HIP could have derived from the physical examination, it is necessary to complete the present trials before population-based screening for breast cancer using mammography can be advocated. Trials are justifiable because the risk of mammographic screening seems likely to be negligible, and the use of the combination of annual mammography and physical examination to be cost-effective. In the meantime, there seems no immediate substitute on a population basis for efficient physical examination of the breasts by primary care physicians coupled with breast self-examination by the woman. Techniques such as ultrasound and diaphanography seem unlikely to supplant mammography in screening, and in any case, have to be evaluated in comparison with mammography.