A patient with asthma due to exposure to ethylenediamine was described. He was exposed to a large number of chemicals used in developing color photographs. He developed a specific and reproducible late asthmatic reaction after occupational-type exposure test to ethylenediamine. Exposure to other chemicals, such as formaldehyde and Kodak developers CD2 and CD3 (p-phenylenediamine derivatives), did not induce any asthmatic reaction. Result of a skin test with ethylenediamine was negative, and precipitating antibodies to this chemical were not found. The late asthmatic reaction was not accompanied by an increase in the venous plasma concentration of histamine. The mechanism of the late asthmatic reaction to ethylenediamine is unknown. An immunologically mediated mechanism cannot be excluded. However, intrinsic bronchial hyperreactivity is probably not an important predisposing factor, because bronchial reactivity decreased and approached the normal range after the patient was removed from further exposure. Ethylenediamine released histamine in studies in vitro from the whole blood of patients as well as in those of 2 unexposed subjects. The role of direct, histamine release in the pathogenesis of asthma has yet to be determined. This is another example of late asthmatic reaction induced by a low-molecular-weight compound.