Abstract: A process for preparing L-carnitine which comprises exposing .gamma.-substituted acetoacetic acid esters or amides to the fermentative enzymatic action of a microorganism which elaborates L-.beta.-hydroxyacyl CoA dehydrogenase [EC 1.1.1.35] , recovering the resulting, optically active corresponding .gamma.-substituted-.beta.-hydroxybutyric acid derivative and converting said derivative to L-carnitine. An improvement in the process is also disclosed which comprises reacting a 4-chloro-3(R)-hydroxybutyrate with sodium iodide or bromide to produce the corresponding 4-iodo- or 4-bromo-3(R)-hydroxybutyrate, converting the 4-iodo- or 4-bromo-3(R)-hydroxybutyrate to the trimethylamino-3(R)-hydroxybutyrate salt, then converting the trimethylamino-3(R)-hydroxybutyrate salt into L-carnitine. Novel chemical intermediates prepared in the processes are also disclosed.