The present invention relates to novel indole-2,3-dione-3-oxime derivatives capable of antagonising the effect of excitatory amino acids, such as glutamate. More specifically the novel indole-2,3-dione-3-oxime derivatives of the invention may be described by general formula (I), wherein R represents "Het", or a group of formula (II), wherein "Het" represents a saturated or unsaturated, 4 to 7 membered, monocyclic, heterocyclic ring, at least one of R , R , and R independently represents hydrogen, alkyl, or hydroxyalkyl, and at least one of R , R , and R independently represents (CH2)nR ; wherein R represents hydroxy, carboxy, alkoxycarbonyl, alkenyloxycarbonyl, alkynyloxycarbonyl, cycloalkoxycarbonyl, cycloalkyl-alkoxycarbonyl, aryloxycarbonyl, aralkoxycarbonyl, CONR R , or "Het"; wherein n is 0, 1, 2, or 3; and R represents phenyl, naphthyl, thienyl, or pyridyl, all of which may be substituted. "A" represents a ring of five to seven atoms fused with the benzo ring at the positions marked "a" and "b", and formed by the following bivalent radicals: a-NR -CH2-CH2-b; a-CH2-NR -CH2-b; a-CH2-CH2-NR -b; a-NR -CH2-CH2-CH2-b; a-CH2-NR -CH2-CH2-b; a-CH2-CH2-NR -CH2-b; a-CH2-CH2-CH2-NR -b; a-NR -CH2-CH2-CH2-CH2-b; a-CH2-NR -CH2-CH2-CH2-b; a-CH2-CH2-NR -CH2-CH2-b; a-CH2-CH2-CH2-NR -CH2-b; or a-CH2-CH2-CH2-CH2-NR -b; wherein R represents hydrogen, alkyl or CH2CH2OH; or a pharmaceutically acceptable salt thereof.