A vaccination trial, performed on 86 3-month-old infants, has shown that the ability of the RIT 4237 live attenuated rotavirus strain to induce seroconversion is dramatically reduced when administered with live poliovirus vaccine. In a subsequent trial performed on 93 infants the attempt to overcome the poliovirus interference by administering two doses of associated vaccines was unsuccessful. No interference by the RIT 4237 strain on live attenuated polioviruses was observed.