Ultrasound contrast agents (CA) consist of stabilized gas bubbles that, when injected intravenously, provide an acoustic impedance mismatch, producing additional contrast to a diagnostic ultrasound scan. These agents must be smaller than 8 mu m in order to pass safely through the capillaries, contain gas for an impedance mismatch and should be stable enough to survive the duration of the imaging session. A double emulsion technique has previously been optimized within our laboratory to create CA with 50:50 poly (lactic-co-glycolic acid) (PLGA). Although a great deal of research has focused on the effects of molecular weight and end capping on solid PLGA particles, very little has been done to examine the effects of these parameters on hollow CAs formed in a double emulsion. Non-end capped PLGA was found to provide maximum enhancement at a molecular weight of 66.0 kDa, giving an ultrasound enhancement of roughly 18.5 dB. The enhancement demonstrated by CA formed using the end-capped PLGA rose to a maximum enhancement of 19 dB at the highest commercially available molecular weight of 82.4 kDa. A strong correlation was seen between ultrasound enhancement, stability under ultrasonic conditions, surface morphology and zeta potential. This study shows the influence of polymer characteristics on the resulting properties of CA and the ability to tailor CAs to particular applications by varying the polymer choice.