The responses of seronegative adults to two live attenuated rubella virus vaccines were compared. Of 50 women who received the HPV-77-DE5 strain, 49 (98%) had an antibody response; the geometric mean antibody titer(GMT) was 1:38 at two to five months and 1:59 at six to 14 months. Of 66 women and three men who received the RA 27/3 strain all (100%) had an antibody response; the GMT was 1:55 at two to five months and 1:75 at six to 14 months. The incidence of mild to moderate transient clinical reactions, occurring in approximately one-fourth of those vaccinated, was similar for both groups. The serologic response to both vaccines was excellent.