The impact of (ZnCl2)22@DAB-dendr-(Pyrr)64 dendrimer on cell viability was the highest for the THP1 line, and the lowest for HeLa and MCF7 cells (Figure2/Table2). However, when comparing these two modified dendrimers, especially the IC50 values, (CuSO4)18@DABdendr-(Pyrr)64 proved to be more toxic than (ZnCl2)22@DAB-dendr-(Pyrr)64, with significant difference in cell viability between the lines tested, except for a very high cytotoxicity occurring for both dendrimers after 48h in the THP-1 cell line. Comparing the cytotoxicity results of PAMAM-Pyrr dendrimers with the cytotoxicity of ion-Pyrr-modified dendrimers, it can be concluded when the almost non-toxic PAMAM-Pyrr dendrimers are modified to gain a positive charge, it results in a significant increase in their toxicity in both neoplastic and non-cancerous cell lines. However, in the case of (ZnCl2)22@DAB-dendr-(Pyrr)64 there is a considerably large concentration range for each the dendrimer is not cytotoxic. Knowing that high transfection efficiency is often associated with high cytotoxicity of dendrimers, which depends on the presence of a substantial number of cationic surface groups in higher generations of dendrimers, we decided to conduct further research for a selected concentration of 10 µM -quite low but oscillating for some lines near the IC50 value. The next step in our research was to find out impact of modification of PAMAM-Pyrr dendrimers with metal ions had on the dendrimers surface charge and whether the charge change was sufficient to form complexes with siRNA.