It is reported on the different forms of the interstitial pulmonary diseases. Apart from the clinical examination the establishment of the professional and hobby anamnesis play an important part for the differential diagnosis. Allergologic and immunologic examination methods may contribute to the etiologic clarification. In unclear findings a bioptic ascertainment is necessary, though histologically not all cases are to be clarified. The author enters the most important clinical pictures and refers to the difficulties of the radiological differential diagnostics. Questions of therapy are briefly discussed.