Young children in day care centers are an important source of hepatitis A virus (HAV) infection. The safety and immunogenicity of an inactivated HAV vaccine was evaluated in 57 children in day care centers. Nonimmune healthy children were given 0.5 mL of vaccine with subsequent doses: group A (28 children), second and third doses 1 and 2 months after the first; group B (29 children), second and third doses at 1 and 6 months. Antibody to HAV was measured before each dose and 8 months after the initial dose. All children developed antibody to HAV. Groups A and B had similar levels of antibody at 2 months; levels were lower in group B before the third dose and higher 8 months after the first dose. Local reactions after vaccination were reported in 17 children (29.8%). Minor systemic side effects that cleared spontaneously were observed in 27 children (47%). © 1995, by The University of Chicago.