Multidrug resistance is a generic term for the variety of strategies that t
umor cells develop to evade the cytotoxic effects of anticancer drugs. It i
s characterized by decreased cellular sensitivity, not only to the drug(s)
employed in chemotherapy but also to a broad spectrum of drugs with neither
obvious common targets nor structural homology, it is one of the major obs
tacles to the successful treatment of tumors. This review concentrates on s
ome of the physiological changes observed in drug-sensitive and drug-resist
ant tumor cell lines that could account for their relative sensitivities to
chemotherapeutics. These changes suggest alternative strategies for combat
ing tumor cells in general and multidrug-resistant cells in particular.