PIP: In order to investigate the incidence of Rh-immunization during a post abortion period of at least 6 months in an Rh-negative mother, Rh levels were treated in 170 Rh-negative women over a period of 6 months. Of 48 women treated with anti-Rho (D)-immunoglobulin, none became immunized. 5 of the 122 women in the control group were actively immunized during this period. Since the risk of immunization increases with gestation length and can occur with abortion, it is suggested that all Rh-negative women who are not already immunized to the Rh factor should receive anti-Rho (D) immunoglobulin after abortion.