Quinazoline compounds which demonstrate antiproliferative activity, such as antitumor activity, processes of preparing these compounds, pharmaceutical compositions containing these compounds, and the use of these compounds. These compounds inhibit the growth and proliferation of the cells of higher organisms and microorganisms, such as bacteria, yeasts and fungi. Preferred quinazoline compounds are capable of inhibiting the enzyme thymidylate synthase. Effects derived from the inhibition of the enzyme thymidylate synthase include those discussed above.