Infant twins sustained severe circumoral and pharyngeal burns from a concentrated solution of benzalkonium (Zephiran) chloride prescribed for treatment of candidiasis. This report emphasizes the unnecessary hazard accompanying use of a potentially toxic drug-especially when prepared in error by the pharmacist-when a safer drug (nystatin) is available for treatment of oral candidiasis. Risks from use of a prescription drug for other than the intended patient are also highlighted by this episode of poisoning.