A novel series of 1,3-dihydro-2H-imidazo[4,5-b]quinolin-2-ones having enhanced water solubility bioavailability and metabolic stability is disclosed in the Formula I ##STR1## wherein R.sup.1 is H, or C.sub.1 -C.sub.4 lower alkyl;R.sup.2 is H, (CH.sub.2).sub.m R.sup.3 ; benzoxazol-2yl, or benzothiazol2-yl;R.sup.3 is C.sub.1 -C.sub.8 alkyl, C.sub.4 -C.sub.8 cycloalkyl, or substituted or unsubstituted phenyl, wherein the substituents are halogen, alkoxy or trifluoromethyl;m is an integer of 1-3; andn is an integer of 1-5;or pharmaceutically acceptable salt thereof.The compounds are useful as inhibitors of ADP-induced blood platelet aggregation in human platelet-rich plasma.