[General observation on drug resistance of cancer cells].

General discussions on the drug resistance of cancer cells were made from various points of view: (1) drug resistance as an unhereditary phenotype, (2) changes in the cell population during drug treatment, (3) acquired resistance and natural resistance, (4) general concepts on biochemical and pharmacological mechanisms for drug resistance, (5) common mechanism for concurrent resistance to DNA-intercalators and vinca-alkaloids, and (6) collateral sensitivity on a cellular basis.