A 4-month-old male infant developed pneumonitis following a prolonged exposure to tear gas (CS or orthochlorobenzylidene malononitrile). The patient had a persistent leukocytosis (white blood cell count 20,000 to 30,000/cu mm) with predominance of lymphocytes on peripheral blood smear and had a slow resolution of the pneumonitis radiologically. A discussion of the toxicity of the two most widely used tear gases—chloroacetophenone (CN) and CS—on the respiratory system indicates that both agents are capable of inducing severe clinical toxicity dependent upon the concentration of the gas.