A phase I trial was conducted to evaluate the safety, tumour and normal tissue localization, pharmacokinetics and radiation dosimetry of Tc-hR3, a humanized monoclonal antibody directed towards the epidermal growth factor receptor, in 12 patients with recurrent or metastatic epithelial malignancies. Patients were injected intravenously with 3.0 mg or 6.0 mg (1010 MBq) of Tc-hR3. Blood and plasma concentrations of radioactivity were measured and a complete 24 h urine collection was obtained. Whole-body images were acquired up to 24 h post-injection and normal organ uptake quantified. Radiation dosimetry was estimated using MIRDose. Safety was evaluated by clinical observation, biochemical/haematological testing and by measuring immune response to Tc-hR3. There were no adverse effects, no changes in biochemical/haematological indices and no immune response to Tc-hR3. Tc-hR3 was rapidly cleared from the blood with a distribution half-life of 10.8+/-3.8 min. The volume of distribution, and clearance, were 180+/-37 ml.kg and 14+/-3 ml.kg.min, respectively. The elimination phase could not be discerned due to increasing blood radioactivity at later times. About 19-24% was excreted in the urine. Normal tissue uptake was mainly in the liver (44-50%), spleen (3-4%) and kidneys (3%). Imaging was positive in one patient with squamous cell carcinoma of the mouth and an involved cervical lymph node. The whole-body radiation dose from Tc-hR3 was 1.34+/-0.02x10 mSv.Bq. We conclude that Tc-hR3 exhibited an excellent safety profile. Future studies to determine the sensitivity and specificity of imaging with Tc-hR3 in a larger group of patients with pre-selection for epidermal growth factor receptor positivity are planned.