In our recent work, we have explored the formation of chemotherapeutic delivery vehicles constructed from four different amphiphilic linear-dendritic hybrid block copolymers. These micelles were found to form about 100-nm-sized structures that were capable of sequestering doxorubicin at loading efficiencies up to 22%. Here, the cellular toxicity of these biocompatible and biodegradable linear-dendritic hybrid materials was evaluated on two breast cancer cell lines and primary human macrophages. The micelles were found not to affect the cellular viability at concentrations below 35 mu g mL(-1). After drug loading, these constructs could deliver an efficient dose of drugs, resulting in significant decreases in cell viability. Kinetic studies indicated that the drug formulation in the poly-mer micelles slowed down the cell uptake compared with the nonformulated drug, but similar efficacy in viability reduction and cell apoptosis were found. Taken together, these linear-dendritic hybrid materials represent an interesting novel architecture for the construction of drug delivery systems. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 217-226, 2012