Female Ra dial workers first employed before 1930 were analyzed for breast cancer mortality and incidence using method and rate tables described by Monson and the Mantel-Haenszel summary chi-square test for significance. Of 1180 located women, 736 were measured to estimate Ra intake. This measured group was analyzed for breast cancer mortality and incidence according to 4 possible risk factors: Ra intake dose, duration of employment, age at 1st exposure and parity. The located women had a mortality ratio of 1.51 (P < 0.05). The measured women showed a significant excess of breast cancer incidence and mortality only among those women with a Ra intake of 50 .mu.Ci or greater. Although the differences were not significant, incidence and mortality ratios were slightly higher for nulliparous women.