The main goal of our study has been to analyze the efficiency of new anticancer drugs, specifically histone deacetylase inhibitors, in tumor cells bearing a multidrug resistance phenotype. We report that the histone deacetylase inhibitors, Trichostatin A and Suberoylanilide Hydroxamic Acid (SAHA), dramatically reduce cell viability and promote apoptosis in different drug-resistant cells, affecting in a much lesser extent to their parental drug-sensitive counterparts. The differential effects induced by Trichostatin A and SAHA between drug-sensitive and drug-resistant cells are reflected on the main characteristics of the resistant phenotype. Thus, reverse transcription-PCR and Western immunoblots confirm that both histone deacetylase inhibitors promote endogenous down-regulation of P-glycoprotein, which is overexpressed in the drug-resistant cells. Transfection of drug-sensitive cells with the P-glycoprotein cDNA ruled out the a priori possible association between apoptosis and down-regulation of P-glycoprotein induced by the histone deacetylase inhibitors. The results suggest a therapeutic potential of histone deacetylase inhibitors in the treatment of cancers with acquired resistance.