Reactions to DTwP vaccine are well known and are a matter of great concern, much for the development of next generation combination vaccines. To avoid such reactions which occur from foreign compounds, WHO suggested manufacture of DTwP vaccine using semi-synthetic medium. The phase III trial reported here was conducted to assess the immunogenicity, tolerability and safety of a new DTwP vaccine manufactured using semi-synthetic medium for both tetanus and diphtheria toxoids in comparison with the routinely manufactured DTwP vaccine.In all, 331 infants aged 6-8 weeks were enrolled, out of which 308 completed the study. The vaccination was done at 6-10-14 weeks following EPI/WHO recommended immunization schedule. Blood samples were collected prior to the administration of first dose and one month after the third dose.Postvaccination, geometric mean titres for each component did not differ significantly amongst the two study groups. Though, the immunogenicity results were comparable between the two vaccines, the incidence of adverse events was comparatively low in semi-synthetic vaccine as against the routine vaccine group for all the three doses.The semi-synthetic DTwP vaccine was immunogenic and showed a significant lower incidence of local adverse events in comparison to the routine vaccine. This vaccine is now being used in the routine vaccination programme both as a triple antigen (DTwP alone) as well as a combination with Hepatitis B and/or Haemophilus influenzae type b vaccine.