Introduction: Single wall carbon nanotubes (SWCNTs) have been proposed for various applications as bioactive molecules: chemotherapeutic delivery, cancer targeting and imaging. However, the question regarding their citotoxicity has not been completely answered. Aim: to evaluate the effects induced induced by this material in different cell lines. Material and Methods: 250 mg/l ss-DNA-SWCNT water solution was obtained through 7 hr sonication. NaCl was added up to the concentration of 0.9%. Dilutions were made to obtain 1, 5, 10 and 20 mg/l concentrated solutions. Tripan Blue protocol was used to assess proliferation in the exposed cell cultures HeLa, HepG2 and PANC-1 cells were exposed to ss-DNA-SWCNT concentrations mentioned above. Measurements were performed after 24 hours from exposure. For each culture a control sample was assigned. Values of control proliferation were considered as 100%. Test samples were calculated and compared as percent of control value. Mann-Whitney, Kruskall-Wallis test were used for the statistical analysis of data. Results: Decrease of proliferation was significantly correlated with dose of administration (p<0.05) for all 3 cell lines. Differences among cell lines at highest concentration (20mg/l) were significant, with higher alterations for PANC-1, intermediate for HEP G2 and lowest for HeLa Cell Lines (p<0.05). Conclusion: Present study indicates that not only characteristics of nanomaterials should be studied, but also the characteristics of the host organism in regard to SWCNT toxicity. Founded by National Grant Contracts: PNCDI-41- 009/2007-NANOPAN and PNCDI 42-115 NANOHEP