Several fatty acids and lysolipids have been shown earlier to increase the permeability of membranes of artificial liposomes, thereby increasing the release of drugs such as doxorubicin (Dox) contained within them. Free fatty acids can also inhibit cancer cell growth in vitro, and it has been suggested that this inhibition results from increased membrane permeability. Clearly, therefore, increased membrane permeability could be used in the design of liposomes for targeted drug delivery. For example, as free fatty acids and lysolipids are released upon phospholipase degradation of the liposome, the liposome could deliver membrane permeability enhancers in addition to the drug to increase the targeted anticancer effect. In this study, we examined the effect on Dox uptake in the breast cancer cell lines MDA-MB-231, MCF7, and MCF7-MDR when incubated with a large panel of different free fatty acids and lysolipids. Dox uptake was quantified by flow cytometry and fluorescence microscopy. We observed no increased Dox uptake in any of the breast cancer cell lines, suggesting that growth inhibitory effects observed earlier subsequent to the addition of free fatty acids to cancer cells are not caused by increased cell membrane permeability.