PCI-34051 is a potent, specific inhibitor of histone deacetylase 8 (HDAC8) with greater than 200-fold selectivity over the other HDAC isoforms, such as 1, 2, 3, 6 and 10. It induces caspase dependent apoptosis in cell lines derived from T-cell lymphomas or leukemias, but not in other hematopoietic or solid tumor lines. PCI-34051 does not cause detectable histone or tubulin acetylation and also does not inhibit growth or induce apoptosis in normal cells such as PBMCs or fibroblasts. Although a phospholipase C-gamma1 (PLCgamma1) defective line is resistant, cells defective in T-cell receptor signaling are still sensitive to PCI-34051 induced apoptosis.