Somatostatin receptor (SSTR) scintigraphy with indium-111 DTPA-octreotide has become a routine diagnostic procedure in oncology. However, it suffers some drawbacks concerning the limited availability, suboptimal imaging properties and elevated radiation burden of (111)In. We have recently been involved in the development of a new tetraamine-functionalised [Tyr(3)]octreotate derivative (Demotate 1) that can be easily labelled with technetium-99m at high specific activities. (99m)Tc-Demotate 1 showed promising properties in preclinical studies. In this study we report on the first experience with (99m)Tc-Demotate 1 in patients. Six patients (mean age 56 years) with carcinoid tumours ( n=2) or endocrine pancreatic tumours ( n=4) with previously positive SSTR scintigraphy were enrolled in the study. Patients were injected with 500-600 MBq (99m)Tc-Demotate 1. Clinical and laboratory parameters were controlled up to 3 months p.i. Blood samples were taken at various time points up to 24 h p.i., and urine was collected up to 24 h. Whole-body images were acquired at 15-30 min, 1-2 h, 4 h and 24 h p.i. with additional single-photon emission tomography imaging at 1-4 h. Blood excretion was very rapid, with <2%ID in plasma after 1 h, and urinary excretion <20% ID after 6 h. Two patients complained of mild gastrointestinal problems and paraesthesia, but no other adverse reactions were observed. SSTR-positive tumours were rapidly visualised as early as 15 min p.i., with maximum tumour uptake (up to 19% ID) and tumour/organ ratios as early as 1 h p.i. Organs of predominant physiological uptake were the spleen and the kidneys, with no intestinal excretion detectable up to 24 h. (99m)Tc-Demotate 1 detected 11 lesions while In-Oct detected ten; differences in uptake behaviour were observed in three patients. This study shows for the first time that peptides derivatised with a tetraamine ligand for labelling with (99m)Tc show suitable properties for receptor imaging in patients. (99m)Tc-Demotate 1 is a promising agent for the visualisation of SSTR-positive lesions in patients, allowing rapid imaging as early as 1 h p.i.; some differences are observed in pharmacokinetic behaviour compared with (111)In-DTPA-octreotide.