The concept of lung diseases caused by the workplace environment dates back to antiquity, but it has assumed considerably greater significance in recent years owing to our expanding industrial environment. Occupational lung disorders represent an important aspect of the pulmonary clinician’s practice, as they cover the whole spectrum of pulmonary diseases, including acute lung injury, interstitial lung disease, asthma, chronic obstructive disease, pleural disease, infectious diseases, and malignancy. <BR> In 1713, Bernadrdina Ramazzini first described asthma-like disorders caused by organic dusts. Occupational asthma caused by inorganic agents was recongized in workers exposed to platinum salts in 1911, and occupational asthma associated with the processing of coffee and castor beans was documented in 1923. With the use of synthetic materials in industry during and after Wold War II, a variety of organic and inorganic chemicals have been found to cause occupational asthma. Over the last two decades, asthma has been increasingly recognized as a major occupational health problem that should receive further medical attention in the future, as it can lead to permanent disability. Furthermore, occupational asthma offers many opportunities to investigate the pathophysiologic mechanisms of nonoccupational asthma and its natural history from on epidemiological point of view. <BR> The purpose of this monograph os to review specific inhalation challenges as a diagnostic tool and an in vivo model to investigate the pathophysiology of occupational asthma and summarizes our current knowledge of this disorders and our personal contribution in this area is presented. The role of specific inhalation challenges in the investigation of occupational asthma is outlined, with a specific focus on our experience of this approach in the identification of causative agents, the investigation of asthmatic reactions elicited by occupational agents, epidemiological surveys and prevention