The aim of our study was to analyse the mitochondrial ultrastructure in primary ductal adenocarcinomas of the pancreas and to compare it with normal pancreatic cells. 52 samples of adenocarcinoma of the pancreas obtained by surgical resection or by endosonographic biopsy were examined. Compared to normal mitochondrial ultrastructure in non-tumorous cells, the mitochondria in cancer cells had a dense matrix and condensed configuration or with lucent-swelling matrix associated with disarrangement and distortion of cristae and partial or total cristolysis. Functionally, these structural alterations presume the presence of hypoxia-tolerant and hypoxia-sensitive cancer cells.