• A bovine rotavirus (strain WC3) was isolated from a calf in Pennsylvania and adapted to growth in continuous Cercopithecus cell line CV1. A pool for human vaccine trials was produced at the 12th cell culture passage level. After preliminary testing in adults and older children, a dose of 3×107 plaque-forming units was given by mouth to 52 infants and children aged 5 months to 6 years. No clinical sequelae were detected, and shedding in feces was detected in only 30% of tested infants. A serum-neutralizing antibody response was induced in 95% of 21 infants aged 5 to 11 months; response rates were slightly reduced in older infants. The antibody response was primarily directed toward bovine rotavirus, but a response to human serotype 3 rotavirus was also observed in approximately 50% of vaccinees. After vaccination with WC3, infants with preexisting antibody to rotaviruses of human serotype 1 or 3 frequently exhibited a booster response to those serotypes. WC3 is a candidate rotaviral vaccine deserving larger trials in children.