Multidrug resistance has for many years attracted attention of numerous investigators. Attempts have also been made to increase efficiency of anti-neoplastic therapy. For this reason, most of efforts have been devoted to analysing proteins engaged in the mechanism of multidrug resistance such as the N-glycosylated membrane protein glycoprotein P. Interestingly, glycosylation probably plays a significant role in the intracellular location and activity of modified proteins. Inhibitors of glycosylation have been demonstrated to alter the activity of glycoprotein P in various ways, depending on the cell line examined. These inhibitors markedly reduce multidrug resistance of cancer cells, thus promoting success of anti-neoplastic therapy. Here, we review the basic knowledge on N-glycosylation inhibitors, their effect on glycoprotein P and their therapeutic potential.