Following the discovery of the very high inhibitory ability of the 4-(3-bromophenyl)aminoquinazolines against the tyrosine kinase activity of the epidermal growth factor receptor (EGFR) (e.g., 3, IC50 0.029 nM), four series of related pyridodpyrimidines bearing electron-donating groups at the 6- or 7-positions have been synthesized and evaluated. The compounds were prepared by nucleophilic substitution of the corresponding 6- and 7-fluoro analogues. While members of all series showed potent inhibitory activity against isolated EGFR, there were important differences between the different isomeric pyridodpyrimidines and the parent quinazolines. Overall, the 3,4-d and 4,3-d series were the most potent, followed by the 3,2-d compounds, with the 2,3-d analogues being least active. Whereas in the parent quinazoline series the addition of steric bulk to a 6- or 7-NH2 substituent (i.e., NHMe and NMe2 groups) dramatically decreased potency, no such trend was discernable in the 3,2-d series. Furthermore, in the 7-substituted pyrido4,3-d- and 6-substituted pyrido3,4-dpyrimidine series, and to a limited extent in the 7-substituted pyrido2,3-d series, such substitution increased potency dramatically, to the extent that the 7-(methylamino)pyrido4,3-dpyrimidine (5f) (IC50 0.13 nM) and 6-(methylamino)pyrido3,4-dpyrimidine (7f) (IC50 0.008 nM) constitute important new leads. Selected compounds were evaluated for their ability to inhibit EGFR autophosphorylation in A431 cells, and a positive quantitative correlation was found between this activity and inhibitory activity against the isolated enzyme.