There is disclosed a process for the preparation of an alpha-aminoketone salt of formula I ##STR1## which comprises reacting a nitrosated keto ester of formula II ##STR2## with a carboxylic anhydride of formula IV ##STR3## under the conditions of catalytic hydrogenation, to a compound of formula III ##STR4## which compound of formula III is then hydrolysed with an acid H.sub.n A to the salt I, in which formulae above R.sub.1 is C.sub.1 -C.sub.6 alkyl, phenoxy-C.sub.1 -C.sub.4 alkyl, phenyl, C.sub.7 -C.sub.9 phenylalkyl, or phenyl or C.sub.7 -C.sub.9 phenylalkyl which are substituted by halogen, C.sub.1 -C.sub.6 alkyl or C.sub.1 -C.sub.6 alkoxy, hydroxy or cyano, R.sub.2 is C.sub.1 -C.sub.4 alkyl or cyclohexyl, n is 1 to 3, R.sub.3 is C.sub.1 -C.sub.4 alkyl and A is the radical of an organic or mineral protic acid.Pyrroles suitable as co-stabilisers for PVC can be prepared from alpha-aminoketone salts of formula I.