Objective: To evaluate the effectiveness and safety of a preparation containing echinacea, propolis, and vitamin C in the prevention of respiratory tract infections in children during a 12-week winter period. Design: Randomized, double-blind, placebo-controlled study. Subjects: Four hundred thirty children, aged 1 to 5 years, were randomized to an herbal extract preparation (n = 215) or a placebo elixir (n = 215). Intervention: Administration of an herbal preparation (Chizukit) containing 50 mg/mL of echinacea, 50 mg/mL of propolis, and 10 mg/mL of vitamin C, or placebo (5.0 mL and 7.5 mL twice daily for ages 1 to 3 years and 4 to 5 years, respectively) for 12 weeks. Results: Significant mean ± SD reductions of illnesses were seen in the Chizukit group in the number of illness episodes, 138 vs 308 (55% reduction); number of episodes per child, 0.9 ± 1.1 vs 1.8 ± 1.3 (50% reduction, P < .001); and number of days with fever per child, 2.1 ± 2.9 vs 5.4 ± 4.4) (62% reduction, P < .001). The total number of illness days and duration of individual episodes were also significantly lower in the Chizukit group. Adverse drug reactions were rare, mild, and transient. Conclusion: A preventive effect of a product containing echinacea, propolis, and vitamin C on the incidence of respiratory tract infections was observed.