The invention relates to substituted 4-(tetrazol-5-yl)-quinazoline derivatives of the formula-I,or pharmaceutically acceptable salts thereof, which possess anti-proliferative activity such as anti-cancer activity and are accordingly useful in methods of treatment of the human or animal body. The invention also relates to processes for the manufacture of substituted 4-(tetrazol-5-yl)-quinazoline derivatives, to pharmaceutical compositions containing the compound and to its use in the manufacture of medicaments for the production of an anti-proliferative effect in a warm-blooded animal such as man.