A double-blind study of women after first-trimester abortion supports the efficacy of low-dose Rho(D) immune globulin (human) in the prevention of Rh sensitization. Twenty-seven per cent of patients demonstrated a fetomaternal blood leak based on Kleihauer-Betke stains. In follow-up testing, the percentage of positive titers and the absolute titer of detectable antibody at various intervals were related to the dose of administered immune globulin. This study confirmed the possible risk of sensitization in Rh-negative postabortal women and suggests the practical use of single low-dose immune globulin preparations in prevention.