The effectiveness of two rubella vaccines (RA 27/3 and Cendehill) in women vaccinated post partum was compared. Significantly more women who received RA 27/3 gave satisfactory seroconversion responses than women who received Cendehill (97.6% vs 82.2%). This difference was reflected in the geometric mean titres (43.6 vs 17.0). More women who received RA 27/3 had minor side-effects, but the difference was not significant. The serological response to both vaccines was not affected by the concurrent administration of anti-D immunoglobulin. In view of these findings, the replacement of Cendehill vaccine with RA 27/3 vaccine for women vaccinated post partum should be considered.