Abstract: The present invention is concerned with the phosphonic acids of formula I ##STR1## wherein one or both of the acidic hydroxy groups of the phosphonic acid moiety may be functionalized in form of pharmaceutically acceptable mono- or di- esters; wherein Y represent optionally substituted 2-carboxypyrrolidinyl, 2-carboxy-2,5-dihydropyrrolyl, 2-carboxy-1,2,3,6-tetrahydropyridinyl, 2-carboxy-1,2,5,6-tetrahydropyridinyl, 2-carboxypiperidinyl, 2-carboxyetrahydroquinolinyl or 2-carboxyperhydroquinolinyl, 2-carboxyl-2,3-dihydroindolyl or 2-carboxyperhydroindolyl as described herein, and in each of which the carboxy group may be functionalized in form of a pharmaceutical acceptable ester or amide; A represents a direct bond, lower alkenylene, lower alkylidene or lower alkylene provided that A does not represent a direct bond when Y represents 2-carboxypyrolidinyl; and pharmaceutically acceptable salts thereof; which are useful for the treatment of nervous system disorders in mammals and as antagonists of the N-methyl-D