A cluster of toxic reactions among children inadvertently given excessive doses of rifampin for chemoprophylaxis of invasive Haemophilus influenzae disease in a day-care center was investigated. In all 19 children, who received five times the therapeutic dose of rifampin, dramatic adverse reactions developed. A striking, "glowing" red discoloration of the skin and facial or periorbital edema were found to be the hallmarks of rifampin toxicity. These clinical signs of acute toxicity contrast sharply with the adverse side effects of rifampin reported with therapeutic doses.