Morpholino-substituted pyridopyrimidine, quinolone, and benzopyranone derivatives inhibit phosphoinositide (PI) 3-kinase, an enzyme that regulates platelet-adhesion processes. As a consequence, the compounds in question have anti-thrombotic activity, as well as other pharmaceutical properties. The compounds claimed are represented by formula (I), (II) and (III). PI 3-kinase generates 3-phosphorylated PI second messengers which stimulate platelet adhesion under blood-flow conditions. Because platelet adhesion is a necessary step in the formation of a thrombus, inhibition by these compounds of PI 3-kinase under such conditions inhibits or prevents thrombus formation. The compounds are useful in treating PI 3-kinase-dependent conditions including cardiovascular diseases such as coronary artery occlusion, stroke, acute coronary syndrome, acute myocardial infarction, vascular restenosis, atherosclerosis, and unstable angina; respiratory diseases such as asthma, chronic obstructive pulmonary diseases (COPD), and bronchitis; inflammatory disorders; neoplasms including cancers such as glioma, prostate cancer, small cell lung cancer, and breast cancer, and diseases linked to disordered white blood cell function, such as autoimmune and inflammatory diseases. ##STR1##