We treated two NB cell lines with single MYCN copy, SK-N-SH and SH-SY5Y, and two NB cells with MYCN amplified, SK-N-BE(2) and KP-N-NS, with three types of broad-spectrum HDAC inhibitors, including short-chain fatty acids (VPA), hydroxamic acids (TSA and SAHA), and synthetic benzamide derivatives (M344), and observed the dynamic correlation between cell viability and the time course of HDACI treatment. The gene discussed is HDAC9; the disease is neuroblastoma.