The Microwave Barometric Radar and Sounder (MBARS) is a new airborne instrument developed to demonstrate the remote sensing capability of atmospheric sea level pressure (SLP) using a combination of a differential absorption radar (DAR) and a microwave radiometer. The MBARS radar is a near-nadir pointing DAR that operates on the upper side of the V-band oxygen absorption feature, with channels around 65.5, 67.75, and 70 GHz. MBARS recently flew a series of test flights and a science flight on the NASA high-altitude ER-2 aircraft. This paper describes the scientific motivation for the development of MBARS as well as the system hardware, aircraft integration, recent flight activities, and retrieval results. Data from recent flights are presented, showing successful SLP retrievals consistent with science requirements and demonstrating potential for spaceborne applications.