The A431 tumor Xenograft was characterized as a model to test EGF-receptor antagonists. Removal of the EGF rich submandibular gland from athymic mice, or stimulation of EGF production in the submandibular gland by testosterone administration both failed to influence tumor growth. Infusion of EGF from alzet minipumps raised circulating EGF levels, however, A431 tumor growth was not significantly changed. Treatment on the other hand (IP every 4 days) with a monoclonal to the human EGF receptor (225 antibody) produced a dose (1-0.25 mg/inj) related inhibition of Subcutaneous (s.c.) implanted A431 tumor growth. Long term inhibition (> 114 days) of tumor growth was related to the number of doses of antibody administrated with 9/10 tumors not re-growing after 9 doses of 1 mg/mouse/inj given 4 days apart. A dose related inhibition of A431 tumor growth when implanted under the subrenal capsule (src) was also established for the EGF-receptor antibody and tumor regression was frequently observed with doses greater-than-or-equal-to 0.5mg/mouse/inj. These studies indicate that A431 tumor growth is insensitive to modulation of host EGF but can be inhibited by agents that block the EGF-receptor. The s.c. and src implanted A431 tumor models that have been established will now be used to evaluate the antitumor potential of EGF inhibitors identified from our screening programs.