The invention relates to .alpha.-amino-N-hydroxy-acetamide derivatives of formula I, ##STR00001## wherein R is di-lower alkyl amino, 1,2,3-triazol-1-yl, 1,2,3-triazol-2-yl or 1,2,4-triazol-4-yl, m represents an integer from 1 up to and including 10, and n represents an integer from 0 up to and including 10, and salts thereof;to processes for their preparation, pharmaceutical compositions comprising said hydroxamic acid derivatives, the use of such hydroxamic acid derivatives as medicaments, and a method of treating conditions or diseases mediated by matrix-degrading metalloproteinases (MMP's) using said derivatives alone or in combination with one or more other therapeutic agents.