Summary

Hypersensitivity pneumonitis is an allergic disease known by its occupational character for over two centuries. Recent researches have elucidated several pathogenic mechanisms, what has made possible a better understanding about the disease. However, hypersensitivity pneumonitis remains quite unknown by physicians, what can lead to imprecise diagnoses. The clinic and occupational histories have an important value because only them can guide the doctor to the definitive diagnosis and the adequate patients’ treatment.