Our previous studies showed that 5-methoxycarbonyl-2-pyrrolidone (pyrrolidone) modified PAMAM G4 dendrimer at the highest concentration of 200 μM was practically non-toxic to three different rodent non-cancer cell lines. While the same concentration of unmodified PAMAM G4 dendrimer resulted in a large decrease in cell viability, up to 90% for the most sensitive cells, after 24 hours incubation. The difference in cytotoxicity between modified with pyrrolidone and amino terminated PAMAM dendrimers is related to the practically neutral surface charge of the former, in contrast to the later having a cationic surface.