A randomized, double-masked, placebo-controlled clinical trial was conducted with 236 preschool children, age 3-6 y, in Indonesia to assess immune status in mild vitamin A deficiency. The immune response to tetanus immunization was used as a measure of immune competence. Clinically normal children (n = 118) and children with mild xerophthalmia (n = 118) were randomly assigned to receive oral vitamin A (60,000 micrograms retinol equivalent) or placebo treatment for a total of four study groups. Two weeks after treatment, children were immunized with diphtheria-pertussis-tetanus vaccine. The immunoglobulin G (IgG) responses to tetanus at baseline and 3 wk following immunization were measured by ELISA. After adjusting for previous tetanus immunization, clinically normal and xerophthalmic children receiving vitamin A had a significantly greater IgG response to tetanus than clinically normal and xerophthalmic children receiving placebo (P less than 0.05). These results suggest that children with mild vitamin A deficiency have a relative immune depression compared with children who have been supplemented to normal vitamin A levels.