An inactivated trivalent poliovirus vaccine, prepared on simian line-cells (Vero cells), has been injected in 3 doses one month apart in 36 infants, 2 to 11 months old (30 of whom were 2 to 6 months old) to determine its tolerance and antigenic efficacy. Each dose contained 40, 8 and 32 antigenic D units for the 3 types respectively. DPT vaccine was injected simultaneously in another part of the body. Before beginning the immunization program, 20 infants had significant titers of antibodies against the 3 types of poliovirus; Only 6 were triple negative. One month after the second dose of vaccine, all the infants had significant titers of antibodies against the 3 types; these titers have not been significantly enhanced one month after the third dose. Two doses of the inactivated vaccine one month apart induced a satisfactory serologic response in spite of the presence of serum maternally transmitted antibodies. There were no adverse reactions.