The aims of this thesis were to investigate the possibilities of antitumour treatment with octreotide and peptide receptor radionuclide therapy with radiolabelled octreotide in the rat. Therefore we used a liver metastases model with somatostatin receptor-positive and somatostatin receptornegative tumours. We also studied the tumour growth stimulating effect of liver regeneration after partial hepatectomy. Since, if this putative tumour growth stimulation by partial hepatectomy could be demonstrated we wanted to see if treatment with octreotide and radionuclide therapy could be effective also after partial hepatectomy and whether this treatment would subsequently influence liver regeneration. In addition we wanted to investigate the value of somatostatin receptor scintigraphy in patients with liver metastases of neuroendocrine tumours to define patients that could possibly benefit from peptide receptor radionuclide therapy.