Proton nuclear magnetic resonance spectroscopy was performed on whole cells to study lipids and metabolites in Adriamycin- and Taxolresistant K562 cells expressing multidrug resistance (MDR) and their sensitive counterparts. With one-dimensional spectra, both resistant cell lines showed lower fatty acid methylene:methyl ratios and higher choline:methyl ratios than sensitive cells. Using two-dimensional COSY spectra, a decrease in the glutamine content was evidenced in resistant cells. When these cells were maintained in culture medium without the drug, the fatty acid signals were partially recovered. Adriamycin-resistant K562 cells were also treated for 4 days with a high dose of verapamil, a MDR-reversing agent. The nuclear magnetic resonance spectra of verapamil-treated cells also showed partial recovery of fatty acid signals. These results could be paralleled with the reversion of the resistant phenotype, as evidenced by measuring the inhibiting concentration of Adriamycin and vinblastine in K562adr cells cultured without the drug or after short-term exposure to verapamil. Conversely, P-glycoprotein and mRNA expression and DNA amplification of the mdr gene were not modified when compared to resistant cells, suggesting that the MDR phenotype could be partially reversed independently of the mdr gene amplification and expression. These results demonstrate the role of lipids in the resistance phenomenon.