This prospective study evaluated human milk and serum antirotavirus antibody concentrations following maternal rotavirus immunization. Postpartum women (33) were randomized into 3 groups and received a single oral dose of rhesus rotavirus monovalent reassortant vaccine (104pfu), tetravalent vaccine (104pfu), or placebo. Milk (secretory [s] IgA) and serum (IgA and IgG) specimens were tested for antirotavirus isotype-specific antibody. Sera also were tested for G1-to G4-specific antibody. Prevaccine milk and serum isotype-specific antibody concentrations were not significantly different in the 3 groups. Postvaccine sIgA log titers were significantly greater in the 2 vaccine groups than the placebo group (P =0.002). Mean log10titers at 1 week were 2.1 (95% confidence interval [CI], 2.0–2.3) in the 2 vaccine groups and 1.7 (95% CI, 1.5–1.9) in the placebo group. Milk titers did not differ between vaccine groups. There was no difference in reactogenicity between groups. The significantly hi