Overexpression of epidermal growth factor receptor (EGFr) in squamous carcinomas has been demonstrated extensively. Preliminary clinical studies have shown that radiolabeled anti-EGFr monoclonal antibodies can localize to these tumors. The aims of this study were to determine the tolerance, pharmacokinetics, and radiolocalization properties of 131I-labeled EGF in patients (n = 9) with advanced squamous lung cancer. Patients' vital signs and symptoms were monitored regularly for 3 days. Daily scintigrams and biological samples for pharmacokinetic analysis were obtained for 3-4 days. 99mTc-labeled human serum albumin was administered to patients with positive tumor scans. Six patients had positive tumor scans, and five of them had received >/=1.0 mg EGF. In all of these cases, tumors were visualized the same day of the infusion, although best tumor-background contrast was obtained at 50-74 h. There were no false-positive images. Whole-body radioactivity retention rose significantly with increasing EGF doses; most labeled EGF was eliminated by urinary excretion. Tumor:normal tissue uptake ratios increased during the course of the study. All patients presented self-limited, dose-related gastrointestinal adverse effects. In conclusion, recombinant 131I-labeled EGF administered i.v. can localize to squamous lung cancer efficiently, can be administered safely to patients, and has more advantageous pharmacokinetic properties than monoclonal antibodies. Further studies are warranted to determine more accurately the potential of EGF and EGF-related peptides in the imaging and/or therapy of EGFr-overexpressing human cancers.