Historical assumptions concerning the optimal fractionation schedules for women with breast cancer are being challenged by the early results of randomised clinical trials. Multiple small fractions of 2.0 Gy or less are optimal for squamous cell carcinomas, which are clearly less sensitive to fraction size than the surrounding dose-limiting normal tissues. Breast cancer may be different in showing comparable sensitivity to fraction size as the healthy tissues of the breast and underlying ribcage. If this is confirmed, it means that fewer, larger fractions confer the same benefit as standard 2.0 Gy schedules, provided appropriate downward corrections are made to the total dose. The approach also lends itself to tests of acceleration, shorter treatment times being of obvious interest to patients and possibly of therapeutic benefit in their own right.