Cryptogenic organizing pneumonia (COP) is a rare, potentially serious respiratory disease which may be idiopathic or secondary to other conditions. Exceptionally, cases of COP of occupational origin have been reported. We present the case of a laboratory researcher who developed COP after prolonged exposure to ortho-phenylenediamine. The diagnosis was made after a specific inhalation challenge (SIC). After clinical and radiological resolution, the patient has avoided the causal agent and remains asymptomatic.