Microbubbles driven by ultrasound are capable of permeabilizing cell membranes and allowing biomarkers or therapeutics to exit from or enter cancer cells， respectively. Unfortunately， the relatively large size of microbubbles prevents extravasation. Lipid-based perfluorobutane microbubbles can be made seven-fold smaller by pressurization， creating 430-nm nanodroplets. The present study compares microbubbles and nanodroplets with respect to their ability to enhance miR-21 and mammaglobin mRNA release from cultured ZR-75-1 cells. Mammaglobin mRNA and miR-21 release increased with escalating concentrations of nanodroplets up to， respectively， 25- and 42-fold with 2% nanodroplets (v/v)， compared with pre-ultrasound levels， whereas cell viability decreased to 62.4%. Sonication of ZR-75-1 cells incubated with microbubbles or nanodroplets caused relatively similar levels of cell death and miR-21 release， suggesting that nanodroplets are similar to microbubbles in enhancing cell permeability， but may be more advantageous because of their smaller size， which may allow extravasation through leaky tumor vasculature.