BACKGROUND Epidermal growth factor (EGF) is normally present as EGF(1-53). A variety of C terminal truncated forms have been used in preliminary trials for treating gastrointestinal injury but their relative potency and stability when used in a clinical setting are unclear. Therefore, we compared the biological activity of recombinant EGF(1-53), EGF(1-52), EGF(1-51), and the C terminal peptides EGF(44-53) and EGF(49-53). METHODS Purity of forms was confirmed by mass spectrometry. Bioactivity of the different EGF forms was determined using [methyl-(3)H] thymidine incorporation into primary rat hepatocytes and their ability to reduce indomethacin (20 mg/kg subcutaneously)/restraint induced gastric injury in rats. Stability of EGF peptides was determined by serial sampling from a syringe driver system containing EGF/4% albumin in saline. RESULTS Biological activity assays of EGF(1-53), EGF(1-52), and EGF(1-51) gave almost identical thymidine uptake dose-response curves (maximal responses increasing baseline uptake from 4400 (600) cpm (mean (SEM)) to about 22 000 (2000) cpm when EGF was added at 1. 6 nM). EGF(44-53) and EGF(49-53) did not stimulate (3)H thymidine uptake. Control rats had 47 (4) mm(2) damage/stomach, EGF(1-51), EGF(1-52), and EGF(1-53) at 0.16 and 0.80 nmol/kg/h each reduced gastric injury by about 50% and 80%, respectively (both doses p<0.01 compared with control but no significant difference between the different forms). EGF was stable at room temperature for seven days but biological activity decreased by 35% and 40% at two and three weeks, respectively (both p<0.01). Exposure to light did not affect bioactivity. CONCLUSIONS EGF(1-51) and EGF(1-52) are as biologically active as full length EGF(1-53) but the C terminal penta- and decapeptides are ineffective. Clinical trials of EGF can probably use infusion systems for at least 48 hours at room temperature and with exposure to light, without reducing biological efficacy.