To evaluate whether the antiproliferative activity of the HDAC inhibitors SAHA and TSA correlates with the expression of zinc dependent HDAC isoenzymes, the potency of both compounds in a panel of 16 human cancer cell lines was determined, expressed as 50% growth inhibitory values (GI50).The 16 cell line panel differed from the previous 17 cell line panel by the removal of the EFM-19 and EPLC-272H cell lines and the addition of the A2780 human ovarian cancer cell line. The gene discussed is HDAC9; the disease is cancer.