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.sup.3 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.sup.31, R.sup.32, and R.sup.33 independendy represents hydrogen, alkyl, or hydroxyalkyl, and at least one of R.sup.31, R.sup.32, and R.sup.33 independently represents (CH.sub.2).sub.n R.sup.34 ; wherein R.sup.34 represents hydroxy, carboxy, alkoxycarbonyl, alkenyloxycarbonyl, alkynyloxycarbonyl, cycloalkoxycarbonyl, cycloalkyl-alkoxycarbonyl, aryloxycarbonyl, aralkoxycarbonyl, CONR.sup.35 R.sup.36, or "Het"; wherein n is 0, 1, 2, or 3; and R.sup.5 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.sup.6 --CH.sub.2 --CH.sub.2 -b; a-CH.sub.2 --NR.sup.6 --CH.sub.2 -b; a-CH.sub.2 --CH.sub.2 --NR.sup.6 -b; a-NR.sup.6 --CH.sub.2 --CH.sub.2 --H.sub.2 -b; a-CH.sub.2 --NR.sup.6 --CH.sub.2 --CH.sub.2 -b; a--CH.sub.2 --CH.sub.2 --NR.sup.6 --CH.sub.2 -b; a-CH.sub.2 --CH.sub.2 --CH.sub.2 --NR.sup.6 -b; a-NR.sup.6 --CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 -b; a-CH.sub.2 --NR.sup.6 --CH.sub.2 --CH.sub.2 --CH.sub.2 -b; a-CH.sub.2 --CH.sub.2 --NR.sup.6 --CH.sub.2 --CH.sub.2 -b; a-CH.sub.2 --CH.sub.2 --CH.sub.2 --NR.sup.6 --CH.sub.2 -b; or a-CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 --NR.sup.6 -b; wherein R.sup.6 represents hydrogen, alkyl or CH.sub.2 CH.sub.2 OH; or a pharmaceutically acceptable salt thereof.