We have evaluated the usefulness of contrast-enhanced ultrasound (CEUS) for diagnosing, staging and assessment of operability of pancreatic head tumors. For some years CEUS has been used with great success for diagnosis of focal liver lesions but when we started our trial, it was still relatively untested in the pancreas. This PhD thesis is based on a methodological study, two clinical studies and an intra-/interobserver study. The methodological study consists of material collected from investigations made on 14 experimental pigs. First, we examined the pig pancreas with CEUS. Hereafter we repeated the CEUS examination after venous injection of the gastrointestinal hormones secretin and cholecystokinin. We investigated if the contrast-enhancement would intensify after hormone stimulation. The clinical studies consist of material collected from examinations of 49 patients referred to our hospital with the diagnosis, suspicion of pancreatic cancer. All patients had a conventional ultrasound examination and a CEUS examination. In addition, some of the patients also had a CEUS examination after stimulation with secretin and cholecystokinin. All patients had a 64-slice-CT examination and a biopsy was taken for histopathological verification. We studied whether CEUS was useful for assessment of tumor classification, tumor staging and tumor resectability. We also tested if hormone stimulation of the pancreas during CEUS could intensify contrast-enhancement of healthy pancreatic tissue and thus contribute to a better demarcation of a tumor. Finally, we tested the intra-/interobserver agreement of our visual interpretation of the contrast-enhanced ultrasound images and the concordance between the visual interpretation and histopathological test results. From the results of the methodological study it seemed possible to intensify contrast-enhancement using the gastrointestinal hormones by 3%. During the clinical studies it emerged that hormone stimulation did not improve the visual impression of the CEUS examinations in any cases. We found that CEUS may be a useful diagnostic tool in the diagnosis of pancreatic head tumors, with a sensitivity of 86% (CI: 79-96) in the diagnosis of pancreatic adenocarcinomas with histopathology as gold standard. Our intra-/interobserver agreements of the visual interpretation of tumor enhancement using CEUS showed substantial or almost perfect agreement with kappa values between 0.75 and 0.89. CEUS was useful for assessment of liver metastases but not as useful for assessment of the local tumor area and thereby not very useful for assessment of tumor resectability. By performing the US+CEUS and 64-CT we additionally found 35% and 45% respectively nonresectable patients of a group of patients, who were considered resectable on the primary radiological image material. In conclusion this thesis points to CEUS as a useful but not sufficient tool in the diagnosis, staging and assessment of operability of patients with pancreatic cancer.