Aims of this study are: (i) to probe a link between some miRNAs and MDR P-gp-mediated; (ii) to improve the knowledge of the pathways involved in cancers characterized by MDR; (iii) to verify if different miRNAs are modulated by P-gp inhibitor and substrate; (iv) to suggest some miRNAs as probes to diagnose MDR and to address chemotherapy. The gene discussed is PGP; the disease is cancer.