Paper presents the effects of the newly synthesized fullerol C60(OH)22 on the growth of tumor cells in vitro and its modulating activity on doxorubicin (DOX)-induced cytotoxicity in human breast cancer cell lines. Cell growth inhibition was evaluated by tetrazolium colorimetric WST1 assay. Electron spin resonance (ESR) "trapping" method was used to investigate OH-radical scavenger activity of fullerol during Fenton's reaction. At a range of nanomolar concentrations fullerol induced cell growth inhibition, which was cell line, dose and time dependent. Fullerol also strongly suppressed DOX-induced cytotoxicity at all concentrations regardless the time of fullerol addition. Proanthocyanidins added as single agent to MCF-7 cell culture for 48 h induced low growth inhibition but in combination with DOX strongly decreased DOX cytotoxicity. Fullerol was found to be a potent hydroxyl radical scavenger: the relative intensity of ESR signals of DMPO-hydroxyl radical (DMPO-OH) spin adduct decreased by 88% in the presence of 0.5 microg/ml of fullerol. The obtained results suggest that antiproliferative effect of the fullerol and its protective effect on DOX-induced cytotoxicity might be mediated through hydroxyl-radical scavenger activity of C60(OH)22.