Rhesus‐human reassortant tetravalent rotavirus vaccine at a titer of 4 x 104plaque forming units was evaluated for immmunogenicity in 194 6–8‐week‐old breast‐fed Turkish infants. The vaccine was administered orally as a single dose following either a meal of breast milk or 30 ml of sodium bicarbonate‐buffered soy milk formula. Four‐fold or greater responses in rotavirus IgA ELISA antibody were detected in 62% and 65′% of the infants in the two groups, respectively (p= 0.62). In a smaller comparison group of non‐breast‐fed infants, an IgA response was detected in 7 of 11 (64%) cases. In all vaccinees, a serological response was detected in 72% of the initially seronegative and 47% of the initially seropositive infants (p= 0.001). We conclude that the take of rhesus‐human reassortant tetravalent rotavirus vaccine in breast‐fed infants is not compromised by breast feeding before vaccination. However, a higher titered preparation of the same vaccine may be required to improve overall immunogenicity in young infants, particularly in those with pre‐vacci