Two groups of children received trivalent poliovirus vaccine. Group B had two doses, 10 to 11 weeks apart. Group A had one dose after 10 to 11 weeks of contact with Group B vaccinates. The second dose increased Group B seroconversions for poliovirus types I, II, and III, respectively, from 87% to 97%, 43% to 69%, and 91% to 100%. Corresponding Group A seroconversions resulting from contact were 25%, 20%, and 52% and increased following a single dose of vaccine to 99%, 60%, and 100%. Children with seven different wild enterovirus infections responded to vaccine type I. Rates of type I shedding after vaccination of children already type I seropositive were approximately 18% for those under 7 years of age and 60% for those under 2 years of age.