Valproic acid, valproate sodium and divalproex belong to the group of medicines called anticonvulsants, used to control certain types of seizures in the treatment of epilepsy. Also, valproic acid relieves histone deacetylases (HDACs) dependent transcriptional repression and causes hyperacetylation of histones in cultured cells and in vivo. Valproic acid inhibits HDAC activity in vitro, most probably by binding to the catalytic centre of HDACs. Most importantly, valproic acid induces differentiation of carcinoma cells, transformed haematopoietic progenitor cells and leukaemic blasts from acute myeloid leukaemia patients. Moreover, tumour growth and metastasis formation are significantly reduced in animal experiments. Therefore, valproic acid might serve as an effective drug for cancer therapy.