The results presented here demonstrate that a cisdiamminedichloroplatinum(II) (DDP)-resistant human ovarian-carcinoma cell line isalso cross-resistant to the spermine analogue N1 ,N12-bis(ethyl)spermine (BESPM). W e report that C13* cells, which are approximately 20-fold resistant to DDP, similarly showed 7-fold resistance to BESPM by colonyforming assay with an IC50 value of 24.6 6 2 mM vs. 3.4 6 0.8 mM of 2008 cells. Resistance appearsto be the result of many effects, such asdifferent morphological and functional modificationsof mitochondria. Furthermore, although BESPM accumulation was almost identical in sensitive and resistant cells, the intracellular polyamine pool of the 2 cell lines was differentially affected by this polyamine analogue. In fact, when spermidine (SPD) was still detectable in C13* cells, in 2008 cells it was not, and the spermine (SPM) content was always more markedly reduced in sensitive cells than in the resistant variant. The lower polyamine content of 2008 cells could be related to a higher degree of induction of spermidine/ spermine N1 -acetyltransferase (SSAT) activity by BESPM in sensitive cellsthan in their resistant counterpart. Despite the observed cross-resistance, the combination of the 2 drugs resulted in supra-additive and synergistic effects in both cell lines, depending on concentration, as assessed by medianeffect analysis of the survival data. The effectiveness of this combination was also confirmed by the increased accumulation of cells in the G2/M phase of the cell cycle in both cell lines. Taken together, these data suggest that BESPM effect on cell growth of DDP-sensitive and DDP-resistant cells involvesmultiple mechanismsthat are differently modulated by the DDP-resistant phenotype.