Through observation of our own patients we have analyzed the problem of differential diagnosis of tumours of the head of the pancreas during operation and have found out that even by means of modern pre-operative examination techniques a clear distinction between carcinomata and chronic panereatitis cannot be achieved. Therefore the final diagnostic decision in these cases is left to the surgeon to be taken during operation. The reservations, generally brought forward against the histological methods of pancreas biopsy (sample excision and Menghini-puncture) because of their low degree of accuracy and high risk of complication, must be confirmed according to our own experience (out of 35 carcinomata, positively diagnosed at a later stage, only 16 had been detected immediately whereas 19 had produced wrong negative results; in 15 cases out of 37 complications had arisen, among them one death). Thus we were looking for adequate methods of cytological diagnosis. Good results could be achieved particularly with curettage of the pancreatic duct and with fine.needle aspiration biopsy (out of t9 carcinomata li definite and 4 suspected positive results). It should be emphasized that so far * Herrn Prof. Dr. W. Baumgartner wird fiir die stiindige FSrderung und das Interesse, das er der vorliegenden Arbeit entgegengebracht hat, herzlich gedankt. Mein Dank gilt auch den Herren Prof. Dr. A. Propst (Vorstand des Pathologischanatomischen Instituts der Universit~t Innsbruck) und Doz. Dr. B. Lederer fiir die morphologische Beurteilung und Befunddokumentation. Teile der Arbeit wurden in Zusammenarbeit mit dem Gastroenterologischen Labor unserer Klinik und mit Unterstiitzung des Fonds zur FSrderung der wissenschaftlichen Forschung in 0sterreich durchgeffthrt. Daf/ir habe ich Herrn Prof. Dr. H. Reissigl und Herrn Dr. :N. Falser zu danken. Schlielllich sei auch Herrn Doz. Dr. E. Semenitz, durch dessen Entgegenkommen die Tierversuche ermSglicht wurden, mein Dank ausgesprochen.