OBJECTIVE To study immunogenicity and reactogenicity of indigenously produced MMR vaccine and to assess the booster effect of MMR immunization on measles seroconversion. METHODS A longitudinal follow up. METHODS Hospital based and home follow up, as required. METHODS 89 children already immunized for measles, between 15 to 24 months of age for immunogenic evaluation and 866 subjects for the reactogenic component. METHODS Prevaccination and postvaccination samples collected one and four weeks after vaccination were studied by ELISA for IgG and IgM antibodies against the three diseases. A clinical follow up of immunized children was done at 3 days, 7 days, 6 weeks and 6 months after immunization. RESULTS IgG positivity 4 weeks after immunization rose from 75% to 100% for measles, from 12% to 92% for mumps, and from 13% to 99% for rubella. Only mild side effects including pain and swelling in 37 (4.3%) cases, mild fever in 51 (5.9%) cases, cough in 40 (4.6%) cases and a transient rash in 7 (0.8%) cases were observed. CONCLUSIONS The indigenously manufactured MMR vaccine has an excellent immunogenicity and low reactogenicity with a booster effect for measles seroconversion in children already immunized for this disease.