We report oil the role of PAMAM dendrimer concentration and generation (102, G4, G6) oil cell growth and cytotoxicity in HEK293T and HeLa cell lines and make comparisons with dendrimer-induced leakage from liposomes to probe the mechanisms in action Specifically, we observed it striking transition from cell growth enhancement to,I reduction in cell viability at a critical PAMAM dendrimer concentration, that is, similar to 500 nM. Confocal microscopy studies show evidence of I transition from cell membrane adhesion to cell Internalization and cell nucleus interaction at equivalent dendrimer concentrations A dendrimer concentration window of 500-700 nM was identified for effective cell Internalization without significant cytotoxicity Though liposome leakage con-elated with cytotoxicity, no quantitative agreement was observed, that is, cells are 100 times (based on surface coverage) more resistant to dendrimers than liposomes These findings have significant implications In the design of effective drug/gene delivery vehicles based oil dendrimers