The aim of this study was to obtain accurate data on the biodistribution of 111In-DTPA-D-Phe1-octreotide in tumour and normal tissues to facilitate dosimetric evaluations. Patients with carcinoid tumours, medullary thyroid carcinoma (MTC), differentiated thyroid tumours, endocrine pancreatic tumour (EPT), breast carcinoma, and various other tumour types were i.v. injected with 111In-DTPA-D-Phe-1-octreotide. Tumour and normal tissue samples were collected during surgery 1-35 days later, and the 111In activity concentration determined. Results showed large inter- and intra-individual variations. The 111In concentration was in general higher in carcinoids and some EPT (range 0.33-77% IA/kg) than in MTC and other tumours (0.017-7.8% IA/kg). Tumour-to-blood ratios (T/B) higher than 100 were found in most patients with carcinoids, EPT, renal carcinoma, and neuroendocrine carcinoma (max value 1500), while T/B was below 80 in most other tumours. Normal-tissue-to-blood ratios were in general < or = 10 but higher values were found in liver, kidneys, and spleen. The results presented are important for dosimetric calculations, when radiolabelled octreotide is used for diagnostic or therapeutic purposes.