When exposed to ultrasound, microbubbles (MBs) deflate [1]. This occurs due to exchange of the MB filling gas with the gas of its environment, thus implying changes in its gas composition. Moreover, recent studies showed that gas composition affects the subharmonic (SH) response of phospholipid-coated contrast agents [2] [3]. In this work we investigated the SH emission from single MBs and the impact of deflation upon insonification.