The present invention relates to serine hydroxymethyltransferase (E.C. 2.1.2.1) as novel target for herbicides, and to nucleic acid sequences encoding a polypeptide with the biological activity of a serine hydroxymethyltransferase, which, when not present, bring about growth retardation symptoms and chlorotic leaves, comprising the nucleic acid sequence SEQ ID No:3, and functional equivalents of the abovementioned nucleic acid sequence or the nucleic acid sequence SEQ ID NO:7 and functional equivalents of the abovementioned nucleic acid sequence. Moreover, the present invention relates to the use of the abovementioned nucleic acid sequences, of functional analogs of the SEQ ID NO:3 or SEQ ID NO:7 or of polypeptides encoded by one of the abovementioned nucleic acid sequences in a method for identifying herbicidally active compounds which inhibit serine hydroxymethyltransferases, and to the use of these compounds which have been identified by the method as herbicides.