(EN) This invention relates to the discovery of substituted analogues of the selective platelet lowering agent anagrelide with reduced potential for cardiovascular side-effects which should lead to improved patient compliance and safety in the treat-ment of myeloproliferative diseases. More specifically, the present invention relates to certain imidazoquinazoline derivatives which have the general formula shown below wherein the substituents have the meanings defined in claim 1: and which have utili-ty as platelet lowering agents in humans. The compounds of the present invention function by inhibiting megakaryocytopoeisis and hence the formation of blood platelets.